Fixing issue with static_url setting overriding the user's since it relied on an or that would eval
to the user's media_url. Also modified the ModelAdmins to only override the MarkdownFields instead of
Textfields so that Textfields display normally unless users specify it as MarkdownField's.
Adding a django_markdown_static template tag that should fix issues with
settings.static_url and load static files properly.
Merge pull request #40 from wldcordeiro/develop

Fixing static_url issue, making package use MarkdownFields instead of Textfields.