Fixed typos and some syntax.

Hi -- the git diff makes this look bigger than it is -- it's mostly single-letter changes.

However, line 139 was "The sender changes the state state of the receiver", and I presumed that "state state" was a typo, and it should just be "state".  It's late at night, forgive me if that's an obvious mistake.

Anyway, thanks so much for doing firesafe!  I'm doing a game with Firebase, and this is pretty much exactly what I need to implement my code.  I'll be following development closely!

Cheers!