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
Initial implementation of descriptions for parameters, which also override their doc strings--in the long term this will be nice for both interactive help and generated API 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
Move names processing from Header to Reader ala include/exclude
Move strict names checking from guess() to apply_include_exclude_names
Add tests of reading tables with names arg given
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
Disable strict names checking when guessing a single reader
When Angle is instantiated with Quantity, equivalence of unit ot radian must be checked.
Added Quantity to Angle conversion test cases.

Angle(1.0*u.deg) should be OK.
Angle(1.0*u.meter) should raise a UnitsError.
Angle(1.0*u.hour) should be converted to Angle(1.0, unit=u.hourangle).