This makes a small change to the C glue code for GameActivity to send
looper wake ups when new input is received (only sending a single wake
up, until the application next handles input).
When a wake up is received and we recognise that new input is available
then an `InputAvailable` event is sent to the application - consistent
with how NativeActivity can deliver `InputAvailable` events.
This addresses a significant feature disparity between GameActivity and
NativeActivity that meant GameActivity was not practically usable for
GUI applications that wouldn't want to render continuously like a game.
Addresses #4
Robert Bragg