ruote >= 2.2.0. Closes gh-7.

Thanks Marco Sehrer.
shuffle admin files
new participant, first iteration
simplification
preparing for exchange options
options rework
'message' option
before :all/:each simplification
spec: deleting queues after use
'persistent' option
'conf' option documentation
'conf' determines option lookup order
rdoc for all the participant's options
a note about Participant#encode_workitem
getting the Gemfile.lock in for now
preparing work on the Receiver
made the :exchange option only accept arrays
minimal receiver
Ruote::Receiver already keeps track of options
Receiver#handle_error(err)

"hook" for errors when handling incoming messages