Added GROUP command support.
wewps: GroupInfo was in wrong package.
Uhhh just a whole lotta stuff here actually.

* Refactored all the things.
* Prematurely optimized all the things.
* Improved the testing of all the things.
* Preparing to support nonstandard yEnc'd + zlibbed compressed OVER response.
Delete stuff made irrelevant by ze refactorings.
Well isn't ResponseDecoder tidy now!