add failing test: savefig(StringIO(), format="ps")
add new ps backend test file in `__init__.py`
Fix writing to all manner of StringIO-like objects in PS backend.
Merge pull request #2512 from mdboom/ps_StringIO

Fix saving to in-memory file-like objects in Postscript backend
Add easy style sheet selection.
Add rc_params_in_file to return partially-filled RcParams

This allows style sheets to update the current settings instead of overwriting them.
Rename style files to `*.style`
Allow style.use to open URLs
Remove pyplot import
Add style context manager and tests
Change style extension to *.mplstyle
Got a little crazy with the whitespace
Add style package and data to setupext.py
Move test so that it actually runs.
Use explicit string check
Hide rc_params_in_file from parent namespace
Remove usage of import *
Clarify docstring
added `matplotlib.style` to pyplot import list
fix url rc specification

smoothed over conflicts

add test for URL stylesheet

whoops, remove extraneous regex I added...

move test to proper location

arg, don't need urllib2 either...didn't realize functionality was in core mpl