Add pry to help debugging during development
Remove unnecessary Griddler::Email#process calls

I'm not entirely sure why these were present, but the tests all pass
without the call. Probably a mistake made early on that was copied
whenever a new test was added.

Since it's not clear from this diff, #process gets the
Griddler.configuration.processor_class and sends it
Griddler.configuration.processor_method with self (the Griddler::Email
instance) as the argument.

This is the first step in moving the process logic out of
Griddler::Email and into the controller.
Move process logic out of Griddler::Email

This is controller code that shouldn't have been in a data object to
begin with.
Use instances rather than class methods

Rather than sending Griddler.configuration.processor_method to
Griddler.configuration.processor_class with a Griddler::Email as an
argument (i.e., EmailProcessor.process(email)), instantiate
Griddler.configuration.processor_class with a Griddler::Email and call
Griddler.configuration.processor_method on that object (i.e.,
EmailProcessor.new(email).process).

This encourages the behavior of separating logic into methods within an
EmailProcessor, which is better than having a single class method with
many responsibilities or passing state around between class methods.