Added KKInputKeyboardBehavior

This makes binding keys to actions ultra simple as a behavior. Simply add the behavior to a `KKNode` or `KKScene`

    KKInputKeyboardBehavior *input = [KKInputKeyboardBehavior behavior];
    [self addBehavior:input withKey:@"input"];
    [input bindKey:@" " toAction:@"jump"];

Then you can check the exact status of a key in any update method:

    KKInputKeyboardBehavior *input = (KKInputKeyboardBehavior *)[self behaviorForKey:@"input"];
    if ([input keyState:@"jump"]) {
        NSLog(@"jump DOWN");
    }
    if ([input keyPressed:@"jump"]) {
        NSLog(@"jump PRESSED");
    }
    if ([input keyReleased:@"jump"]) {
        NSLog(@"jump RELEASED");
    }