input/yuv.cpp is CSP un-aware

[Steve Borho]

The output/yuv.cpp file correctly uses the csp table to know the number of planes and the sizes of each one. The input side needs the same changes.

This is a one-day job, but needs to be done well.

[Steve Borho]

yuv: support colorspaces in YUV input files (closes #13)

→ <<cset 13dac38f54ac>>