[Fix] Allow requests to actually send JSON (or hopefully XML).

- First off, who's really gonna use the XML? I didn't really test with that, but JSON seemed to be working for what I was doing and the tests pass.
- Set the proper headers to actually send JSON or XML and then send JSON or XML instead of http_build_query every time (format sensitive and falls back to the old behavior).
- Remove code that made it look like you could actually pass a curl handle and all that stuff. It wasn't being used and looked funny.
- Fixes #4.