Add new examples and some code cleanups

I've renamed pingpong.c to msg_pingpong.c to reflect the EP type. All the rma tests have been merged into one example to keep it simple. I will be adding some more examples.
rtt_factor looks like it's really number of transfers per iteration.  If so, then xfers_per_iter may be a more meaningful name.  I'm not sure what 'rtt' stands for.