PROTON-781: Provide the PN_RBREF and RBREF constant values.
PROTON-781: Added the Event and EventType classes to the Ruby engine APIs.

Also the set of related events used by applications.
PROTON-781: Added the Event and EventType classes to the Ruby engine APIs.

Also the set of related events used by applications.
PROTON-781: Added the Collector class to the Ruby engine APIs.
PROTON-781: Created the Endpoint mixin for the Ruby engine APIs.
PROTON-781: Added the Container class to the Ruby engine APIs.

Also includes supporting classes for a priority queue, events and
timers.
PROTON-781: Added Ruby examples for the Reactive APIs.