Rackless exception handling

Re: Issue #17

We created a rackless exception handler that inherits from exception handler and overrides handle and initialize in order to take messages that aren't rack specific.

We also created a rackless issue renderer that would return a title based on the class#method that is passed to RacklessExceptionHandler, and passed back a set of optional params.

This seemed to work really well for us with Sidekiq, and would probably work well for any other rackless environment.

Both classes have tests that cover the new functionality.