Taps close together allow us to change modes.

After the die is awakened by a tap, a single tap will display the
current mode (with both decimal points on so we can tell that this is
the mode rather than a roll), then after 1.5 seconds it will begin a
roll.  If there is a tap inside that first 1.5 seconds, it will change
mode, display that mode, and wait a further 1.5 seconds.  If that 1.5
seconds times out, it does a roll.

Signed-off-by: Russell Steicke <russells@adelie.cx>