Add the ability to specify XSLT filename by path relative to any given available egg

[mitchellrj]

As an alternative to specifying filename or tree in your WSGI configuration, one may specify an egg resource in the form:

egg_name:path/to/resource

[lrowe]

When running as WSGI middleware python:// urls are supported (but poorly documented...). This gives you the ability to use a url like: python://myprojects.package/static/foo.html when referring to any resource. See: https://github.com/plone/diazo/blob/master/lib/diazo/wsgi.py

Reopen this if you thing there is some functionality in your patch missing here.

[mitchellrj]

Ah, it seems I inadvertently altered the wrong part anyway, my intention was to support the 'rules' variable in this way. It seems that python:// URLs don't work in this instance, so I will resubmit a different pull request shortly.