Function frames

frames(
sourceVideoEl: HTMLVideoElement,
opts?: FramesOpts,
): AsyncIterable<ImageData>
Generator that yields frames from a video element as ImageData.
```
import { Video } from 'https://unpkg.com/ixfx/dist/visual.js'

const ctx = canvasEl.getContext(`2d`);
for await (const frame of Video.frames(videoEl)) {
  // TODO: Some processing of pixels

  // Draw image on to the visible canvas
  ctx.putImageData(frame, 0, 0);
}
```
Under the hood it creates a hidden canvas where frames are drawn to. This is necessary to read back pixel data. An existing canvas can be used if it is passed in as an option.

Options:
- canvasEl: CANVAS element to use as a buffer (optional)
- maxIntervalMs: Max frame rate (0 by default, ie runs as fast as possible)
- showCanvas: Whether buffer canvas will be shown (false by default)
Parameters
- sourceVideoEl: HTMLVideoElement
- opts: FramesOpts = {}
Returns AsyncIterable<ImageData>