Add Planck 2013 cosmology

* Add Planck2013 cosmology object.  Not the default because
  not yet published.  More Planck results are not expected until
  2014, so hopefully the name is safe.
* Mention Planck2013 object in documentation.
* Add very minor unit test for Planck2013.
Update Planck13 reference, correct omega_8 value.
Fix #908, broken by #865.  Makes show_progress == False work correctly
updated what's new in index to v0.3
Merge branch 'master' into astropy

Merges up through r2072

Fixes #256, #309

Conflicts:

	astropy/io/fits/hdu/compressed.py
	astropy/io/fits/tests/test_core.py
	astropy/io/fits/tests/test_diff.py
	astropy/io/fits/tests/test_image.py
	astropy/io/fits/tests/test_table.py
	astropy/io/fits/util.py
Merge pull request #917 from iguananaut/fits-merge

Merge branch 'master' into astropy
Fixes issue #864 reasonably well; you'll still get a traceback if some extension modules outright failed to compile--that is, this doesn't help with a broken installation. Just with the not too uncommon case of someone trying to 'import astropy' from a source checkout
Merge pull request #864 from iguananaut/issue-864

import coordinates: cannot import name sofa_time
Merge pull request #908 from mdboom/console/hide-download-progress-fix

astropy.utils.data.download_file() crashes when show_progress=False
Reference a couple more fixes that were merged into the v0.2.x branch
Follow up to aea5e7ec, the fix for #864. Added a missing word from the command users should run
Merge pull request #923 from eteq/whats-new-v0.3

updated what's new in index to v0.3
Merge pull request #895 from aconley/planck13

Add Planck 2013 cosmology