Auto repeat for left and right keys

Auto repeat for left and right keys

Key repeat effect is implemented in two phases.
First phldase is to decrease rcDelayMs reciprocal to hold time.
When rcDelayMs reached a certain limit (scheduling interval),
repeat rate will not raise anymore, so we call key handler
multiple times (repeatCount).

XXX Caveat: Most constants are adjusted pragmatically.
XXX Rewrite this someday, so it uses actual hold time instead of
holdCount, which depends on the scheduling interval.