Buffer protocol assumes single plane

[mikeboers]

This works fine for packed data (e.g. rgb24), but segfaults on planar data (e.g. yuv420p).

Need to decide if we want to export each plane as their own buffer, or somehow pack them.

[mikeboers]

I have created a VideoFormat which allows for easy inspection of formats and components.

I propose the buffer protocol on a frame returns the first plane, and a planes attribute exposes the width/height of that plane along with its buffer.

[mikeboers]

We now have planes exposed on video and audio frames.

Could use a nice high-level API, but it now aligns with FFmpeg.