Fixes #121

This aims to prevent extending UserDefinedFunction for UDFs whose translation
is very simple (e.g. different name in SQL, different argument order, etc).

Fixes #115

This commit reverts commit 89418d13.

The reverted commit will be applied in another branch (probably 'adql-2.1') as
it is part of the next release of ADQL-Lib.

- Now, `ADQLParserFactory.createParser(...)` should be used to create a parser
- Only the new function `LOWER` is supported for the moment
- Not yet possible to manage the optional features _(next dev to come)_
=> 1st step for ADQL-Lib v2.0

- TAP adapted so that using the last stable version of the ADQL language
  (i.e. 2.0 for the moment)
  - but not yet possible to set the ADQL version to use in the configuration
    file

This new function - ADQLParser.tryQuickFix(...) - fixes the most common issues
with ADQL queries:

- replace Unicode confusable characters by their ASCII/UTF-8 version,
- double-quote SQL reserved words/terms (e.g. `public`, `year`, `date`),
- double-quote ADQL function names used a column name/alias (e.g. `distance`,
  `min`, `avg`),
- double-quote invalid regular identifiers (e.g. `_RAJ2000`, `2mass`).

The last point is far from being perfect but should work at least for
identifiers starting with a digit or an underscore, or an identifier including
one of the following character: `?`, `!`, `$`, `@`, `#`, `{`, `}`, `[`, `]`,
`~`, `^` and '`'.

It should also been noted that double-quoting a column/table name will make it
case-sensitive. Then, it is possible that the query does not pass even after the
double-quote operation ; the case would have to be checked by the user.

Finally, there is no attempt to fix column and table names (i.e. case
sensitivity and/or typos) using tables/columns list/metadata. That could be a
possible evolution of this function or an additional feature to implement in the
parser.

As @vforchi said:

> The ANSI standard `||` is supported only by Oracle and Postgres: MySQL uses
> `CONCAT` and SQLServer uses `+`.

_This commit resolves the issue #70 ._

Follow up to the commits 33a790a4
and 5e0f82de

In TestPgSphereTranslator, two strings are compared
containing (double) floating point numbers. These numbers are slightly
different with different Java versions. To overcome this, only the
first eight fractional digits are compared.

* The parsing did not allow unsigned numerics and SQL SET functions as
  specified in the ADQL 2.0 grammar

* It was even forbidden to put a column whose the type is not String.

* The translation of a concatenation expression was always prefixed by the
  ADQLList's name: CONCAT_STR. Of course, no database likes that...

Regarding this last point, this commit fixes the GitHub issue #54

if the alias is not delimited in ADQL.

This commit fixes the GitHub issue #56

this table is declared with an alias. Instead, the table alias must be used.

Note: This problem occurred only when ADQLParser was used with a DBChecker.

This commit fixes the GitHub issue #53

A delimited identifier is any sequence of characters between a pair of
double quotes. For instance: "123 I am a delimited identifier!".

It is of course possible to have double quotes inside this kind of identifier,
but they have to be doubled in order to not be mistaken with the end of the
identifier. For instance: "Cool ""identifier""".

However, this escape option was not taken into account by the ADQL library,
though the same mechanism was already in place for string contants.

reserved word is encountered instead of a column/table/schema name/alias.

On the contrary to the previous commit, this time a list of SQL reserved words
has been added into the ADQL grammar. In this way, the parser will ensure that
no word of this list is used in an ADQL query. The raised error is then enriched
of an HINT message stating that this word is part of SQL, is not supported
by ADQL and must be written between double quotes if used as an identifier.

The list of SQL reserved words comes from the ADQL-2.0 standard, after removal
of all potentially used ADQL words, in order to avoid a conflict with the
already existing tokens in the ADQL grammar.

reserved word is encountered instead of a column/table/schema name/alias.

No list of ADQL reserved words has been added into the ADQL grammar.

However, the ADQL grammar has been slightly changed in order to provide a more
precise location of the REAL wrong part of the query.

Before this commit, if an ADQL reserved word (e.g. 'point') was encountered
outside of its normal syntax (e.g. 'point' no followed by an opening
parenthesis), the next token was highlighted instead of this one. Hence a
confusing error message.

For instance, the following ADQL query:

```sql
SELECT point
FROM aTable
```

returned the following error message:

> Encountered "FROM". Was expecting: "("

Now, it will return the following one:

> Encountered "point". Was expecting one of: "*" <QUANTIFIER> "TOP" [...]
> (HINT: "point" is a reserved ADQL word. To use it as a column/table/schema name/alias, write it between double quotes.)

This error message highlights exactly the source of the problem and even provide
to the user a clear explanation of why the query did not parse and how it could
be solved.

with a different local charset, the error message will print differently the
incorrect character.

and HashMap more generic by returning resp. a List and Map instead.

In the resulting SQL query, if there are an alias on the joined tables, these
aliases must be used in the ON clause (instead of the full table name).

For instance, the following ADQL query:

```sql
  SELECT *
  FROM tableA AS a NATURAL JOIN tableB AS b;
```

should be translated into the following SQL:

```sql
  SELECT *
  FROM tableA AS a
    INNER JOIN tableB AS b
      ON a.id = b.id
```

This commit complete the resolution of the Pull Request #16
(more details about the issue can be got in there)

when an incorrect character that can not be interpreted by
the JavaCC Token Manager is encountered.

Actually, the TokenMgrError thrown by JavaCC is caught by all
ADQLParser.parseQuery(...) functions, wrapped inside a ParseException
which is finally thrown instead of the TokenMgrError. In this way,
ADQL-Lib users just have to care about a single Throwable:
ParseException.

Besides the error message has been slightly modified from:

> Lexical error at line 1, column 10.  Encountered: "\u00e9" (233), after : \"\"

to:

> Incorrect character encountered at l.1, c.10: \"\\u00e9\" ('é'), after : \"\"

Thus, the error is more user-friendly, more easy to understand by users.
Additionally, the incorrect character is displayed, as before, in its unicode
expression, but also in its character form (instead of an integer value that
nobody can really understand).

This commit fixes the GitHub issue #17

This infinite loop occured only when the replacement object is just
a wrapping of the matching object ; after replacement, the new object was
inspected for matching objects.

Example: infinite loop if we want to wrap all foo(...) functions with
         the function ROUND in the following query:
    SELECT foo(foo(123)) FROM myTable
	     Expected result:
    SELECT ROUND(foo(ROUND(foo(123)))) FROM myTable
	     But generated result was:
    SELECT ROUND(ROUND(ROUND(......foo(foo(123))))) FROM myTable

See the test case TestDBChecker.testClauseADQLWithNameNull() for more details.

since the commit 8e2fa9ff.

(https://github.com/gmantele/taplib/commit/7a70c6038cef460ab169682bed391bb5ae1de1e9)

It was not possible to use a GROUP BY with a qualified column name.
So finally, now, a GROUP BY is a ClauseADQL<ADQLColumn> instead of
a ClauseADQL<ColumnReference>. Indeed, according to the ADQL's BNF,
GROUP BY items are only columns as they would appear in the SELECT
clause (i.e. qualified or not, delimited or not). On the other
hand an ORDER BY accepts ONLY column index or non-qualified column
name/alias.

The class ColumnReference is kept for backward compatibility (or in
case the next version of the ADQL grammar make items of GROUP BY and
ORDER BY of the same type: index or qualified column). Besides, this
class is still inherited for the ORDER BY clause items
(see adql.query.ADQLOrder).

a qualified column name should be allowed, but still no column index should be.

This error has been raised on the issue #32 by Zarquan.

the automatic datatype detection was missing for CENTROID functions.
--
Additionally, some JUnit test files of the `adql` package has been moved to
the correct location.

The "normal" JOIN:
    A JOIN B ON A.id = B.id JOIN C ON B.id = C.id
is correctly interpreted as:
    ( (A JOIN B ON A.id = B.id) JOIN C ON B.id = C.id )
But with a NATURAL JOIN, the tree is mirrored:
    A NATURAL JOIN B NATURAL JOIN C
gives:
	( A NATURAL JOIN (B NATURAL JOIN C) )
instead of:
    ( (A NATURAL JOIN B) NATURAL JOIN C )
This is not a problem when the SQL translation is identical to the ADQL
expression, but for some DBMS a conversion into a INNER JOIN ON is necessary
and in this case we got the following SQL:
    A JOIN B JOIN C ON A.id = B.id ON B.id = C.id
Which seems to work, but is syntactically strange.

This commit should fix the generated tree. A "normal" JOIN and a NATURAL JOIN
should now have the same form. A JUnit test has been added into TestADQLParser
to check that: testJoinTree().

sub-query. Without this information, it was impossible to resolve columns makingreference to sub-queries of the clause FROM. See the JUnit test case for a
concrete example.
(error raised by Hendrik Heinl - ARI/GAVO)

in DBType.DBDatatype (for UNKNOWN and UNKNOWN_NUMERIC). This reset is performed
after each JUnit setting a special custom value (otherwise it prevents other
JUnit to run correctly)

Before correction, if an ADQlObject (e.g. a function or a sub-query) contains
another ADQLObject and that both (i.e. parent and child) are matching in a
SimpleReplaceHandler and are asked to be replaced, only the parent
seemed to have been replaced. However, the child has been replaced, but
in the former instance of the parent ; and so its replacement is not
visible in the final query.

For instance:
if all mathematical functions must be replaced by a dumb UDF named 'foo' in
the ADQL query:
        "SELECT sqrt(abs(81)) FROM myTable"
,the result should be:
        "SELECT foo(foo(81)) FROM myTable"
,but before this correction it was:
        "SELECT foo(abs(81)) FROM myTable".

deals with NATURAL JOINs and JOINs using the keyword USING so that being
supported by SQL Server. Basically, they are translated as a list of ON
conditions.
Warning: This translator is just guaranteed to solve the NATURAL and USING
issue. Support for datatypes conversion and case sensitivity has to be
reviewed. Besides no geometrical function is translated for SQL Server.

This is easily possible for concatenations, string constants and User Defined
Functions having a FunctionDef. A new special datatype was needed for
numeric functions and operations: UNKNOWN_NUMERIC. This special type
can not be set with FunctionDef.parse(...) and it behaves exactly like the type
UNKNOWN, except that DBType.isNumeric() returns true (as .isUnknown()).
Thus, while writing the metadata of a result in TAP, nothing changes:
an UNKNOWN_NUMERIC type will be processed similarly as an UNKNOWN type:
to use the type returned from the database ResultSet or to set VARCHAR.
(no modification of TAP was needed for that)