Transfer animation from one AdvancedSkeleton rig to another

Before I joined the project, the player character in Toca Days went through many different iterations with varying proportions, and even after the design was locked in place, the rig went through several versions before reaching its final state. Some of these versions having wildly varying joint and control orientations (!!!). But during this time animation was also being created, so once we reached a "final" rig we had lots of animation that needed to be transferred to it. The regular ways to transfer animation were not giving good enough results, so I created a small tool to do it! The tool uses temporary constraints between the "from rig" controls and the "to rig" controls, setting a keyframe on a "to control" only when its "from control" has a key to make a usable timeline.