Pymoc

- Prevented an error reading an ASCII MOC file with an order with
an empty cell list. As of MOC 1.1 this should encode the MOCORDER
if higher than the greatest stored order. This module does not (yet)
process this information but it should now be able to read such
files without error.

- Prevented an error when reading an empty ASCII MOC file.

- Updated a docstring which refered to the now deprecated Astropy
FITS HDUList.writeto method clobber argument.

- Skipped calling the Healpy "query_disc" function for catalogs
if the given radius is zero (or less).

- "pymoctool" now accepts "-" in place of a filename to read from
stdin or write to stdout in ASCII format.

- Improved speed of MOC generation from catalogs by making use of the
Healpy "query_disc" function. Additional optional arguments can be
given to the "catalog_to_moc" function to control this process.

- "pymoctool" now checks that a running MOC is present for some commands.

- Corrected bug reading MOCs in FITS format on 32-bit systems with
64-bit NUNIQ columns.

- Corrected bug in intersection routine.
- Added option to skip validation of cell numbers in the "add" method.

- Added utility to create MOCs from catalog files.
- "pymoctool" can now invoke the plotting and catalog utilities.
- Preserve metadata read from FITS file when constructing new MOC object.