Improve the QuickTime spec

[marcin-osowski]

I plan to extend it more, but I'd like to send out this chunk of work first, to check that I'm doing this right.

Changes:

1. Updated URLs to Apple documentation.
2. Added docs
3. Implemented the matrix field
4. Added duration in seconds
5. Added two new atoms (there's a lot more in the spec)
   • Media header (mdhd)
   • Handler reference (hdlr)

[marcin-osowski]

Friendly ping.

[marcin-osowski]

Thanks for the improvements, they look good to me.

I don't fully understand the syntax in d8fce6b1fceb0695b1bb0106764e9d2927dd335c, though, but I guess it's all good.

[generalmimon]

I don't fully understand the syntax in d8fce6b1fceb0695b1bb0106764e9d2927dd335c, though, but I guess it's all good.

Most of it (the doc key) is just human-readable documentation with some Markdown formatting (more precisely CommonMark) - the syntax there is not important, the content is.

The value instances are described in the User Guide, but I guess you aren't asking about them, given that you used them too.

[marcin-osowski]

I see, I was puzzled by for example -orig-id, but I see that those are just keys which names start with -: https://doc.kaitai.io/user_guide.html.

Looks good to me!

[generalmimon]

I have a few small suggestions:

[marcin-osowski]

Thanks for the suggestions, and the very detailed research! I updated the pull request, I hope I didn't miss any of your proposals.