Move test dependencies to gemspec
Yield event in base capture methods
Refactor how Rack exceptions are captured

The interface is Raven::Rack.capture_exception. The implementation
uses the new yield behavior of Raven.capture_exception to avoid
needing a special-case capture_rack_exception on Event or to
manually send the event.

For parallelism, define Raven::Rack.capture_message as well. See
the next commit for a use case.
Add Raven::Rails::ControllerMethods
Merge pull request #85 from jfirebaugh/controller_methods

Add a mixin for capturing exceptions/messages from a Rails controller