Expose Sinatra `use` statements for modifying the middlewares

This adds a `use` method to `Deas::Server` that will take
middleware configurations. These `use` calls are stored up and
piped to the Sinatra application, allow middleware to be added
as it normally would with Sinatra.
Merge pull request #24 from redding/jcr-add-middlewares

Expose Sinatra `use` statements for modifying the middlewares