Initial user and instrument docs. (#396)

Cassini ISS

===========

The Cassini Imaging Subsystem comprises two instruments -- a narrow angle camera

and a wide angle camera.  The narrow angle camera contains 24 filters, and the

wide angle camera contains 18 filters.

Processing Cassini ISS Images

-----------------------------

    import ale, json, os

    from ale.drivers.cassini_drivers import CassiniIssPds3LabelNaifSpiceDriver

    from ale.drivers import JsonEncoder

    # Use the images to generate ISDs and create CSM cameras

    # Assume images are in current directory

    nac_stereo_1 = 'N1702360370_1.LBL'

    nac_stereo_2 = 'N1702360308_1.LBL'

    def generate_isd(filename):

        driver = CassiniIssPds3LabelNaifSpiceDriver(filename)

        # SPICE kernels are furnished inside this with

        with driver as d:

            # this is the information for the ISD in a python dict

            aledict = d.to_dict()

            # Export python dictionary ISD to external json file to be used by CSM

            alelabel = os.path.splitext(filename)[0]+".json"

            with open (alelabel, "w") as file:

              json.dump(aledict, file, cls=JsonEncoder)

            return aledict

    # Generate ISD and export to a json file

    nac1_dict = generate_isd(nac_stereo_1)

    nac2_dict = generate_isd(nac_stereo_2)

    # Construct a camera

    camera1 = csm.create_csm(nac_stereo_1)

    camera2 = csm.create_csm(nac_stereo_2)

Dawn FC

=======

The Dawn Framing Camera is a frame camera with a resolution of up to 25 meters

per pixel.  This instrument contains a clear filter and 7 band-pass filters.

Processing Dawn FC Images

-------------------------

Galileo SSI

===========

The Galileo Solid State Imager is a modified form of the Voyager Narrow Angle

Camera.  Galileo SSI has 8 band filters and is capable of capturing imagery with

a spatial resolution up to 1 kilometer per pixel.

Processing Galileo SSI Images

-----------------------------

Hayabusa ONC

============

The Hayabusa Optical Navigation Camera is suite of three instruments (two wide

angle and one telescopic imager), and is primarily used for navigation.  The

wide angle cameras employ clear filters, and the telescopic imager uses 7

color filters and one clear filter.

Processing Hayabusa ONC Images

------------------------------

JunoCam

=======

JunoCam is a push frame camera attached to the Juno spacecraft.  This camera

uses four filters and has an intended spatial resolution between 3 and 15

kilometers per pixel.

Processing JunoCam Images

-------------------------