Audit Mode Formatter Integration

@mcquin 

Right now I only have the STDOUT formatter tied into the event bus.  I'm going to add the JSON formatter and update this review, but I wanted to get it started.
I don't like having a class variable to keep track of the events in the run_context.  But I don't have access to the list of formatters once they are passed in, and I don't have access to calling the initialize method - RSpec handles that.  Any other ideas for how I can pass the events into here?