Merge pull request #553 from peastman/docs

Lots of cleanup to how documentation gets built

docs/usersguide/conf.py

@@ -49,9 +49,9 @@ copyright = u'2008-2014, Stanford University'
 # built documents.
 #
 # The short X.Y version.
-version = '6.0'
+version = os.getenv('OPENMM_VERSION')
 # The full version, including alpha/beta/rc tags.
-release = '6.0'
+release = os.getenv('OPENMM_VERSION')
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.