Combine the render-loop wait with the button press wait

[carlosmn]

Instead of doing non-blocking read followed by some sleep, we can combine the
time we want to wait until the next render cycle with waiting for the button
presses.

This means that even with slow rates, aka long sleep times, we can still react
quickly to button presses.

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Testing locally it does work though I don't know if there was some reason for the loop to be the way it is right now. Beyond the first iteration it shouldn't matter whether the button change detection is the first or last thing as the sequence is still going to be the same.

[TheJebForge]

The loop was like that, because I didn't realize I could just wait with the timeout of read_buttons. It does have a consequence, where if a plugin uses frame counting or something like that, their thing will skip forward on a button press. But I think I'll just add to the docs that you shouldn't rely on anything, but elapsed time since start.

Using the timeout though makes the actions much more responsive, even if the pool rate is at 10. I think, I'll be able to decrease the pool rate to 100 now. I had it at 1000 apparently, so buttons would react instantly, and it didn't used much more CPU.

[TheJebForge]

I think I have no problems merging this, thanks!

[carlosmn]

Cool yeah, relying on cycle timings for animations causes issues for games etc as well.