Adds Flask-Classy to extensions registry
Merge pull request #740 from apiguy/add_classy_ext

Adds Flask-Classy to extensions registry
Added a new release
Fixed HTML validation issues on front page
Use new-style ext imports
Added requirements.txt

Unsure about the version numbers -- i determined the deps through trial
and error.
Use pythonhosted.org instead of packages.python.org