add docs/_themes
- correct error when building docs in Sphinx:
Warning, treated as error:
~/projects/pyramid/pyramid/docs/api/i18n.rst:6: WARNING: error while formatting arguments for pyramid.i18n.TranslationStringFactory: 'function' object has no attribute '__bases__'
Merge pull request #1236 from stevepiercy/master

Allow 1.5b docs to be built in Sphinx