[WIP] ABCv6 bug fixes, QoL, and documentation

[Five-Damned-Dollarz]

The big change is that it now pulls vertex animation data directly from the mesh as it's animated, so no more name-binding shape keys to animations! You also no longer have to have a "d_" action for every action you don't want/need vertex animations on.

Fixed:

• 26

• Vertex animation import having incorrect frame matchups (only happened with huge amounts of shape keys, >1000)
• Armature selection in the export window not actually allowing you to choose
• Shape keys no longer bleed onto other animations if they're not all reset to 0 value at the end of an animation

[haekb]

Oh sorry, notifications for PRs seem to be off 😅

Thanks for the update!

[haekb]

Didn't see the WIP tag at first (need more coffee.) But fixes look like they work just fine. Feel free to throw any additional prs if anythings broken.

Cheers