Support for batch request processing

Inspired by: https://developers.facebook.com/docs/graph-api/making-multiple-requests/

It is sometimes beneficial to make a single roll-up request, rather than requiring an implementation to make multiple over-the-network requests.

My initial PoC only required modifications to the parseRequest and onRequest methods. I can PR what I have if you want to take a look and offer any feedback.

If you want to drop in a gist of your PoC I'll be happy to look it over. I'm not opposed to the idea as long as we're adhering to standards and best practices.

@atuttle , my colleague @sammud-sharma and I have been working on getting a working PoC in place. It's mostly functional, though things like file uploads haven't been ironed out. We wanted to make sure this direction was something you were cool with before we put a ton of time into it:

https://github.com/sammud-sharma/Taffy/commit/8b28f03b548dad7c034891764cf7e487f3df37c5

Thanks!