Support for keyframe-based animation in IQM instead of fixed framerate

[RicardoLuis0]

Size for files with long animations can be an issue (gzdoom only supports iqm for skeletal animations), how possible is it to add a new version of iqm (3?) that uses keyframes for animations, instead of a fixed framerate?

(this is mostly to ask how open the spec is to a new version)

[lsalzman]

The idea would be to make an IQM extension, rather than a V3.

The extension could hold the necessary keyframe data, or some way of how to interpret the frame data as if it was keyframe data.