Animation blending

[MarcusLongmuir]

(Requires element & attribute spec)

Requirements:

• Ability to transition between two animations without gaps (e.g. returning to T-pose)
• Ability to blend animations using weights
• Ability to play multiple animations (e.g. punch and run)
• Ability to specify animations within an addressed file that contains multiple animations (currently anim of m-model only allows using the first animation in a file)
• Ability to modify the playback speed of animations (and allow the playback speed itself to be animated using m-attr-anim and m-attr-lerp).