Add support for NROWS and NCOLS
Add support for PVTYPE
Add IREP support

Also refactor PVTYPE support to avoid a hack in fixed length texts.
Add support for ICAT
Add PJUST support
Add ICORDS and NICOM support

These don't really do anything yet, since we don't implement the follow on parsing.

Also add some exceptions if we ever hit a not-yet-implemented case.
Add support for IC
Add support for image compression, image coordinate representation and start of image band