Enable coverage testing and publishing to coveralls.io
For Python 2, fix the paths to use the source files, otherwise coverage report is full of temporary file paths.
Activate optional dependencies
Merge pull request #1604 from astrofrog/coveralls-io

Use coveralls for astropy
Merge pull request #1605 from mdboom/wcs/upgrade-4.19

Upgrade to wcslib 4.19
Merge pull request #1565 from mdboom/setup/display-commands

Running ``python setup.py egg_info`` should not install Numpy
Merge pull request #1616 from mdboom/unit/sorted_ordering_of_bases

BUG is_equivalent for units sometimes fails
Add missing parameter descriptions in Time and TimeDelta
Merge pull request #1621 from taldcroft/time/fix-class-docs

Add missing parameter descriptions in Time and TimeDelta class docstrings
Fix for unnessary path elemnts in timer docstring

[ci skip]
Fix table masking and filling example
Merge pull request #1626 from taldcroft/table/mask-docs

Masking example broken in table docs
Fix rst doctests in table package
Restore masking.rst doctests now that #1626 fixes it