Fix typo in doctest
If running in an msys shell, use the /home/embray environment variable set in that shell to find the user's home.  The surest way to determine this is if the MSYSTEM environment variable is set (it doesn't matter what it's set to).  Obviously this isn't foolproof but there are few better alternatives (one might be to try calling 'uname').
Add function to calculate inverse of cosmology function and tests
Raise a NotImplementedError when fitting composite models.
clarify error message
add changelog entry
use correct PR number
Fix typo in doc string

uncertaintys -> uncertainties
Add changelog entry
updates based on feedback
minor doc updates
add description of z_at_value along with some other minor clean-ups
Attempt to calculate delta_ut1_utc when the attribute is accessed directly
Fix test failures introduced by doc changes
more changes to address travis build failures
More explicit setting of jd1,jd2 in _get_delta_ut1_utc
Add bug-fix entry to CHANGES.rst
Add support for OGIP format units.
Add warning that `Wcsprm` should not be used to get the original values
of keywords in the header.
Call `set` from within the WCS constructor.