Added support for Input ",", as well as wrapped values so <0 goes back to 255

Howdy,

Comma now works by showing an input box above the source when necessary and pausing interpretation until a value is entered.

I also made numbers wrap around so incrementing 255 sets the cell to 0, and decrementing 0 sets the cell to 255 to make them more byte-like.

Some of the indentation got messy in the interpreter.js and emacs just fixed it up automatically for me like that, hope that's alright.

Cheers,
Dave