Add Waifu2x support

[spillerrec]

waifu2x-converter-cpp as a C library interface, and while not as good as the actual Lua based Waifu2x, it should do the trick.

Hopefully it shouldn't be too bad to implement, but there should be an option to not compile with it as I'm not sure circleci will have it as a package, and I don't want to start having to build it manually.

[spillerrec]

I have a RGB float32 version up and running, needs to be cleaned and have the YUV and Y versions as well though.
It needs a folder path to point towards the models, which obviously will differ depending on the computer. It appears it has to be specified, though the waifu2x-converter-cpp executable must have a way to deal with this.
And lastly, there is a blockSize parameter which I do not know what does. It seems to work with it being set to 0 at least.