change default from np.median to np.ma.median
Add 0.4 what's new section about coordinates

Also adds a  doc ref that was needed in docs/coordinates/representations.rst
updated coordinates to stable status
Update status for astropy.cosmology and astropy.convolution
Typo fixes from @mdboom's suggestions
added missing space

[ci skip]
Update coordinates What's New to emphasize positive new features

- Moves most of the original content into a new section "Migrating
  from pre-v0.4 coordinates" in the main coordinates index page.
- Adds a sphinx note up top pointing to the possible need for
  migrating code with a link to the new section.
Fix docs typo
Merge pull request #2680 from taldcroft/whats-new-04-coordinates2

What's New 0.4 coordinates - take 2
Merge pull request #2678 from astrofrog/update-stability

Update status for astropy.cosmology and astropy.convolution
Merge pull request #2677 from eteq/coordinates-stability

updated coordinates to stable status
Updated docstring to say that fields are not stripped
Update this test to provide a little better information when it fails.
Merge pull request #2682 from amras1/fix-tab-docstring

Changed docstring of tab-separated values reader
Added a note to system packagers, where hopefully they can find it
Fix how terminal size is handled in table.pprint.
Raise exception when running tests inside IPython.
Make tests pass on Scipy 0.12.1
Fix #2685.
Merge pull request #2686 from mdboom/modeling/scipy-0.12-tests

Make tests pass on Scipy 0.12.1