create immediate mode animation for tsoding

[ratchetfreak]

this time a more compact pull request.

The core logic is that the Anim struct holds 2 timestamps

• currentTime which is the point at which the animation is in (incremented every frame with delta time)
• clipStartTime which is the at the point in the linear code

the clipTime function then remaps current time from the interval [clipStartTime, clipStartTime+duration] and returns a value between 0 and 1 for use in interpolation.