Add Frame Pacing Utility

[rmorshea]

The following will allow animation callbacks to produce frame with relatively consistent timing.

import time
import asyncio


class FramePace:
    
    def __init__(self, rate):
        self._rate = rate
        self._last = time.time()
    
    async def wait(self):
        await asyncio.sleep(self._rate - (time.time() - self._last))
        self._last = time.time()

[rmorshea]

closed by #37