Add support for pure-markdown pages

[ryanvilbrandt]

Users should be able to use pure markdown to add pages to their website. We can allow this by creating something like a md_page.tpl template that uses base.tpl and inserts any parsed markdown below the links bar.

User will still need to specify the pages to be published in the [Pages] section of comic_info.ini, largely because they'll need to specify titles to be passed to base.tpl.

Markdown files (*.md) can be stored either in the "templates" directory, or in a separate directory like "pages". Make sure to check the theme directory first.

Extra credit:

• Add config option to specify which what the default template to use for parsing markdown is.
• Add config option to specify what options the markdown parser runs with
• Enable the meta section in the markdown to let markdown pages call out which template file to use.

[ryanvilbrandt]

This will be available in 0.4.0.