Introducing a RST like documentation parser

This pull request is related to #45. 

This adds a RST like documentation parser for more control over the data to show within swagger.
It also adds a documentation formatter setting that allows users to use markdown or some other format for the method descriptions.
Also the settings system is reworked so that it looks more like the one used by django-rest-framework.

I don't think there are any BC breaks within this code.

Using the RST like syntax issues like #20, #19 and #37 should be easy to fix.

I Hope you have some time to take a look at this. 

Cheers!