Support validating Django templates by compiling them

This automatically assembles test cases for every template under a template directory and compiles it.  I used this for a large refactoring to find a few path updates I missed but I imagine it would be handy for other things too.

I'm happy to add tests for this if you can help me figure out how to do that.  :-)

If you don't want to merge this, please let me know so I can break it out into it's own package.  Thanks!