added test_imports to make sure all packages successfully import
added open_api_page function
Initial version of the astropy.constants docs
Add equivalency for f_nu <-> nu * f_nu
Add equivalency for f_lambda <-> lambda * f_lambda
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`