This patch implements 'autoRepeat' functionality for `keyboard.down`.
With this patch, the subsequent calls to `keyboard.down` would generate
an event with 'autoRepeat` flag set to true.
Closes#157
VolumeUp, VolumeDown, and VolumeMute were changed to AudioVolumeUp, AudioVolumeDown, and AudioVolumeMute
The media keys like MediaTrackNext were also missing, so I added them.
This patch starts waiting for double raf after every mouse event.
It looks like a good enough workaround to make sure mouse events
are delivered.
The single raf might not be enough because browser might 'return' an already-prepared
frame for us without actually dispatching events.
Closes#122
