Update to use new Scotty 0.5.0 transformers.

Here is a patch that allows scotty-hastache to use Scotty's new transformer stuff. You'll probably want to review my definitions of `runH` and `runActionToIO` to make sure what I did with the state is correct. (It appeared that the state wasn't saved at the end of each action, so I didn't do that.) In this case, you could probably use a simple IORef instead of an MVar.

I've updated the example and tested it. I haven't tried to see what needs changing in interactive-diagrams.