YUV formats

This crate implements conversions from YUV/YCbCr formats to RGB. It also contains enums/constants for describing color spaces common in video formats.

Currently it's in an early stage, implementing subset needed for decoding AV1/AVIF.

Implemented

• Matrix conversion for BT601, BT709, FCC, BT470BG, SMPTE240
• YCgCo (untested)
• Identity pass-through (GBR)
• Studio and full range colors
• 8-bit, and 10/12 to 16-bit conversions

Planned

• Gamma conversion
• Color primaries conversion
• Chroma upsampling
• RGB to YUV conversion
• YUV pixel convenience functions, like in rgb
• 8-to-16-bit expanding conversion
• HDR to SDR conversion?
• Maybe HDR support?