#65 Add turbo toggle

[Ben Whitman]

I use a gamepad to play the games, and it would be REEEEAAAALLLLY nice if there was a toggle for turbo, rather than separate buttons, or even better, a setting for each button separately to either toggle or use a separate button (especially helpful in per-game setups) for games where you might want to hold a certain button while rapid-firing another one. Then I could just toggle on the turbo with, say the return key and keep playing with my controller like normal. You could even put in a turbo for the D-Pad (can't think of any games where you'd want it, but who knows? ;P).

-Q