Adds a clear method to reset the DB (#321)

        obj = cls(adjacency, node_id_map=adjacency_lookup, config=config)

        return obj

    def clear(self, tables=None):

        """

        Truncate all of the database tables and reset any

        autoincrement columns to start with 1.

        Parameters

        ----------

        table : str or list of str, optional

                the table name of a list of table names to truncate

        """

        session = Session()

        session.rollback() # In case any transactions are not done

        if tables:

            if isinstance(tables, str):

                tables = [tables]

        else:

            tables = engine.table_names()

        for t in tables:

            session.execute(f'TRUNCATE TABLE {t} CASCADE')

            try:

                session.execute(f'ALTER SEQUENCE {t}_id_seq RESTART WITH 1')

            except:

                session.rollback()

        session.commit()

        session.close()

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