added test_imports to make sure all packages successfully import
include all cosmology functions as methods of the cosmology object
remove now-incorrect sentence from cosmology docs
Added a section on using setup.py develop.  This will provide a good segue into talking about virtualenv. Will also add the suggested docs for trying out a PR
Added a basic overview of using virtualenv
Add some notes on virtualenvwrapper and venv; fix some minor sphinx syntax issues
Here are some additional notes on using virtualenv with IPython
This is a mostly trivial change, but it's also more consistent--if the other unit conversions in this class are using abbreviations why shouldn't lightyear? Alternatively, both versions could be made available (i.e 'lightyear' and 'lyr', likewise 'pc' and 'parsec', etc.)
Add WMAP9 cosmology.

* Add 9 year WMAP cosmology from Hinshaw et al. 2012 (arXiv 1212.5226).
* Because this paper is on arXiv and not yet refereed/published, leave
  WMAP7 as the default.
* Add a WMAP9 test to get_current in test.
Minor fix to parameter values

* Previously, Oc0 was Oc h^2 / h^2, but table 4 actually gives
  Oc0 directly, and it's slightly different.  This is presumably
  due to the vagaries of the actual distributions for h and Oc0 h^2.
Add missing ) in source for WMAP9 cosmology.
Got rid of references to './setup.py' per @astrofrog's comments. I still used to just 'setup.py foo' when referencing specific setup.py commands, but wrote out 'python setup.py' when discussing full commands run at the command line.
Update astropy.time setup to allow using system sofa_c library
Related to #618, this adds a What's New section for units and quantities.
As per #618, adds a "What's New in 0.2" section for `io.votable`.
As per #618, adds a "What's New in 0.2" section for `wcs`
An alternative to the fix in #634. This forces the use of Distribute so that
we don't generally have to worry about supporting Setuptools.  This is Good
because although Setuptools and Distribute are both a mess, the latter fixes
several bugs that remain unfixed in the former, and includes features we rely
on such as 2to3 which are not backwards compatible with Setuptools.

The fix in #634 is slightly misleading because simply calling
`import setuptools` does not, in all cases, imply that the "system distribute"
is being used.  The "system distribute" is in fact not well-defined because it
depends on knowing the default installation path for Python packages on the
particular OS in use.

This approach simply checks to see if there's already a Distribute installation
on the Python path and forces it to be used over Setuptools if a potential
conflict exists between them.  It only uses disribute_setup if no version of
Distribute is available at all.
Use imp.reload instead of relying on the reload() builtin.
Add note to changelog about this pull request.
Added long-form and short-form versions of all the unit conversions.  Also added 'redshift' as a long-form for 'z'.  Not sure if that's really necessary though since I think 'z' is pretty well understood.  I'm also not sure how I feel about spelling out 'astronomical_units' but I put it in for completeness.