Adding Promise.fromDeferred helper to wrap jQuery Deferreds

RSVP is a great - thoroughly clear and small enough that it can be used as a fundamental abstraction across all my JS.  I'm mostly working browser-side and mostly using $.Deferred now, and was surprised that it didn't chain the way I expected.  In surveying the landscape, I didn't find a good fit, mostly for the same reasons you mentioned in http://news.ycombinator.com/item?id=4662222.  So thanks!

I'm not sure if this fits with your goals for the project, but I think the idea to add helper functions that can wrap other promise abstractions into RSVP.Promises would be helpful in adopting it in my projects.  This pull request adds that helper function for wrapping $.Deferred and is similar to #4 which wraps functions using Node-style callback parameters.

This is a little extra cruft (and basically useless for the Node build), so maybe this works better as an extension that is part of the project but a separate output of the build.

Thanks!