Depend on redcarpet for Markdown parsing.
Add 404 error page as static file.
Add sinatra/namespace as dependency for dashboard routes.
Add configurable posts route.

Posts will be behind a /prefix route to avoid querying the database for
both pages and posts when hitting and /* route. The prefix is configurable
in the main config.yml file. This change lets users hit the posts controller
via the user's chosen prefix as well as /posts/posts_path.

In the future, we'll allow the prefix path to be empty which removes the
prefix (which some consider ugly) from post paths but will add server load.
Rename the markdown parser to MDParser as Parser caused a naming conflict.
Fix issue where Post has wrong association type.

Was many_to_many. Is now many_to_one.
Add methods to populate data from request.
Fix errors in view rendering.
Trying to get build to pass.