WSGIScriptAlias support

This is intended to provide the [WSGIScriptAlias directive](http://modwsgi.readthedocs.org/en/latest/configuration-directives/WSGIScriptAlias.html) to make it possible to host wsgi applications with this module. This also addresses issue #137, but using the latest templating system (which appears to have been refactored since @grimborg's pull request).

I've added some documentation and tried to conform to the style of the rest of the module. If you have any comments/suggestions/etc, I'm happy to make the necessary changes.

Thanks for providing a great module!