Why are we using imread instead of fread as done in MaSIV?

[raacampbell]

fread will give us a 40% speed boost, so why not use it? Should go over the loader again and test.

[raacampbell]

Actually: PK5D is even faster: https://github.com/abcucberkeley/PetaKit5D

I have benchmarked their code at 3x faster than imread.