Adapters for Backbone.js events

Introducing `msgs/adapters/backbone` which contains the
`inboundBackboneAdapter` and `outboundBackboneAdapter`. These adapters
can listen for or trigger (respectively) events on Backbone objects.

inboundBackboneAdapter:

- The first argument to the adapter becomes the payload, the full
  arguments array is available as the 'args' message header.
- If the specific event to listen for is not defined, 'all' events are
  subscribed.

outboundBackboneAdapter:

- The 'events' option is required. As common in Backbone, a space
  delimited string can be used to specify multiple events.
- The 'apply' option can be used to treat an array payload as individual
  arguments to the event trigger

See http://backbonejs.org/#Events

Issue: #11