Add sphinx docs and theme
Describe TemplatedEmailMessage a little better
Describe CleanEmailBackend
Add docs build directory to gitignore
Escape asterisks
Add docs to manifest
Merge branch 'docs'

* docs:
  Add docs to manifest
  Escape asterisks
  Add docs build directory to gitignore
  Describe CleanEmailBackend
  Describe TemplatedEmailMessage a little better
  Add sphinx docs and theme
Include test templates in manifest
Test with tox
Add travis config and badge