Implement texture cache (not in Cycles mainline)

[boberfly]

The Tangent Animation branch has a working texture cache using OpenImageIO:

https://github.com/tangent-animation/blender278
https://www.youtube.com/watch?v=_2Ia4h8q3xs

See if we can make a special feature branch with Cycles

[skwerner]

I have moved the texture caching branch from the Tangent repository to the Blender repository now:
https://git.blender.org/gitweb/gitweb.cgi/blender.git/shortlog/refs/heads/cycles_texture_cache

[boberfly]

@skwerner hey you've found this github, cheers for the heads-up!