Control & Fullscreen improvements!

Made some minor improvements today:

• Added control instructions to the page banner (most are obvious, but this is a reminder that you can CANCEL or access the MENU on touchscreens with a two-finger tap - I received a question about this from a player)
• Made a small optimisation that improves the game's performance in full-screen mode. I've added instructions to the banner to show how to get into fullscreen mode too.

As always, any problems, give me a shout.