27 before request callback

[xentek]

• adds support for a before callback, which is automatically fired before matching requests on a resource
• a single before callback can be applied to multiple request methods (:get, :post, et al)
• before callbacks take a version, much like request handlers do
  • this branch also fleshes out version'd resource support so that it actually works as intended, including determining the requested version
• adds an unrelated change to add an option for forcing ssl (will be used later to configure rack-ssl automatically)
• adds specs to many areas of the code that were untested
• punted on adding after callback support, for now

refs #27