d66fa60fcf introduced the use of a timer
to coalesce screen updates. This is OK, but it does introduce update
latency.
To help mitigate the impact of this, we now have a second (immediate)
timer. When a compose pass is first triggered, the immediate timer will
allow the compose to happen on the next spin of the event loop (so, only
coalescing updates across a single event loop pass). Any updates that
trigger while the delayed timer is running, though, will be delayed to
that (~60fps) timer.
This fixes#103.