add color_transfer in video and count streams

[sapsan4eg]

No description provided.

[vansante]

Adding the ColorTransfer field is fine by me 👍 .

I am however not sure all that extra counting code is worth the effort when you can just do:

// Assume this is the returned data from the command
var p *ProbeData

// to count all video streams:
count := len(p.StreamType(ffprobe.StreamVideo))

You could argue that your counting code is more performant, because it does not allocate a new slice, but I expect the number of streams to be < 10 in most common cases.

[vansante]

You might want to rebase on v2 to fix the CI ;)

[vansante]

Has been added by #54