Optimized Center of Rotation skinning in unity

The majority of this code is not mine - it comes from CodeKiwi on the unity forums (link)

this is a wip repo that i only recommend looking through if you hate yourself. im actively working on making it more user friendly and faster (its currently about 83% the speed of built in skinning)

I also plan to include shaders for all render pipelines. the current provided shaders are for built in, but expect the hdrp shaders to be the most fleshed out