Started work on changing simd c-types from simdN to simdNrealX or simdNwordX

Currently after compilation my version of mlton fails because it can not find the
correct names for my simd types. While I was going to attempt to parameterize them
I decided instead to just write out the 6 needed types and use those.

I also decided to make SimdReal a seperate structure that SimdSize, and use that
when refrencing any SimdReal data. I may change the name to SimdRealSize