27 before request callback

- 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