Problem: we don't support zgossip yet

* Started work on zgossip (New, Bind, Destroy)
* Added initial tests
* Added zgossip_msg.xml file

Note: I will be making a new version of the zproto go templates that work with goczmq.  The initial goal will be to support codec generation and goczmq will still use the zgossip C api for the actual actor.  The secondary goal will be to allow creation of state machine based services directly in go using zproto, but that is a longer term goal.