Updated urls.py and utils.py to get rid of deprecation warnings

[NickHurst]

Update to get rid of deprecation warnings. Stopped using patterns() in urls.py. Changed ctx in utils.py to a dictionary rather than a context. Used mark_safe on the extra_settings parameter to prevent escaping.

Added conditional from #60 to handle different django versions when calling markdown preview.

[marshallds]

I'm currently using @NickHurst's branch in production since it includes the Django 1.9 compatibility fixes. Would be nice to be able to go back to the mainline in my requirements.txt though.