Request params, upload support

[jonson]

I've sucked up a few changes from the android-async-http project (https://github.com/loopj/android-async-http). Namely, support for request params, I find the standard httpclient params cumbersome to work with.

Also, they've added multipart upload support, something that should be included in the platform IMO. Before finding their stuff, I was previously including multiple jars to support this.