Promise support

[Rand McKinney]

There have been some questions about LoopBack's support for promises.  Partial support is in place, and we're working to finish it.  We're tracking the work in issue  #418.

At this point, documentation is minimal: https://docs.strongloop.com/display/LB/Using+promises.

We plan to update API docs to include promise APIs, as well, but that hasn't been done yet.  See #1409 for the doc tasks.

Thanks,

Rand