Refactor wcs to use six
Merge pull request #1372 from hamogu/fixlatex

fix bug in writing AASTex tables
Disable range check for degrees_to_dms and hours_to_hms
Merge pull request #1405 from mdboom/unit/coverage

Improve astropy.units test coverage
First attempt at IERS A, B table classes, interpolation of UT1-UTC.
Cleanup of logical vs integer, use of super.

Correct bug introduced with previous commit
Memoize IERS_A and IERS_B: tables can be kept for session.
Initial linkage to time, with only simple exception messages.

Correction to linkage to Time
First test cases -- if for nothing else than stop me from some silly mistakes
Cleanup of interfaces

Cleanup of interfaces
Moved IERS-B data and both readme's to data subdirectory
Adapt setup_package.py to include iers/data files
Add documentation, some tests, ensure ReadMe's work on .gz files
Simplified Time part; added IERS A tests; document how to use A if needed
Remove documented trickery that's unlikely to remain (or be needed).
Next iteration: exception in ut1_utc, safer memoization
Corrected doctest examples
Provide get_delta_ut1_utc method to Time; update documentation
Updates of documentation and doctests / simplification of get_delta_ut1_utc
Fix trivial typo in table documentation.