Install csrf_token() for all template types.

This installs csrf_token() in the render context so that
it works by default for all template types, not just Jinja2.

Also adds a test for the helper function and bumps the version
number.
Merge pull request #112 from longhotsummer/master

Install csrf_token() for all template types.
PEP8 fix for csrf.py files. Fix tests for Python 3