Add registry.get_formats() function to return table of formats
Check for no formats matching input data_class
Auto-update unified I/O class read and write docstrings to show available formats
Include available formats in exception message for read/write fail

Some minor comment additions and docstring update as well.
Fix minor doc mistake
Add deprecation of short-form ascii format names
Add formats table to unified I/O docs
Make doc update work without pre-existing formats table
Fixes so that test_registry tests pass
Fix Python 3 failure when updating docstring
Rename variable has_read to has_readwrite for clarity
Added regression test for Numpy bug in Python 3 prior to Numpy 1.6.2
Add a known issue for the sorting in Python 3 with old versions of Numpy
Skip Table.sort tests that fail in MacOS X with Python 3 and Numpy < 1.6.2
Sort formats table by Deprecated column to put them at the end
Print available formats table when format could not be identified
added a pretty-print wrapper for coordinates
RA should print as hours if sexagesimal printing used
format -> to_string
completely changed coordinates.to_string to accept common style formats