[cpp] Endpoint application properties

From Alan:

"""
Connections, sessions and links can all have application defined properties. C++ and Go lack options to set these and accessors to read the remote properties.

Python has the old style:

c.properties == local properties, must set before open.
c.remote_properties == remote properties

Ruby has a :properties option to open, and an accessor:
c.properties == remote properties

I guess C++/go should follow ruby - a properties option for each endpoint type and a properties accessor that returns the remote props?
"""

API spec proposal:
http://home.apache.org/~jross/pumpjack/core/endpoint-options/properties.html
http://home.apache.org/~jross/pumpjack/core/endpoint/properties.html