Improve Scratch 2.0 support

I did some work on Scratch 2.0 support for you. I'm not sure if it's ready for you to merge to master yet (ie. a pull request may not actually be appropriate). I do recommend cloning this fork and playing around yourself.

In particular, Scratch 2.0 doesn't seem to make GET requests for reporters *at all*. It's very odd.

I *didn't* do support for Scratch 2.0-style parameters, which is the thing you really wanted. :P Sorry. (I did leave in a useless `get_route` function by mistake. Sorry. I can't fix that right now.)

NB: You need to use the offline player.