modification as discussed in pull request
add more assert statements to tests
Fix typo
Implement an IPAC table writer

This is based on discussions in #833 and and #1143.
@taldcroft
@keflavich
Please use this pull request to suggest your changes.

closes #833
fix itendation errors in documentation
Refactored HDF5 reader, path can now be to a group or dataset, and if no path is specified, the first table found will be read. If more than one is found, a warning is emitted.
Refactored HDF5 writer, use recursion to simplify logic
PEP8 fixes
Added HDF5 tests to ensure good coverage
Fix --coverage for Python 3.x
Manual rebase -- allow sigma_clip by axis
Add TimeGPS class to Time (=seconds since 1980-01-01 00:00:00 UTC = TAI - 19 s
Fixes to .travis.yml to get correct wheels
Switch to a known working pip version
Fix bug that occurred in decompose because for Numpy arrays, the value was being passed by reference rather than by copy, and for Quantities with a non-unity scale, this modified the value of the original Quantity
Introduce units.cycle as part of astropys.py
(rather than si.py, since cycle is a non-SI unit recognised for use in
astronomy: http://www.iau.org/science/publications/proceedings_rules/units/)
Merge pull request #1120 from hamogu/fix1120

Fix bug where Table.remove_column was converting a masked table to unmasked
Add test that u.cycle.to(u.rad) is close to 6.28...
Updates to documentation to clarify the meaning of GPS time
modified for the suggetions on the pull request