batched f16 conversion

[johannesvollmer]

(and also fix round up division missing documentation)

@Shnatsel will this approach work in terms of optimization? i had to add a few copy operations for technical reasons

to do:

• [x] unit tests
• [x] before and after benchmark
• [x] add documentation about how to unlock all the optimizations (compiler flags and such)
• [x] use newest half dependency
• [x] clean up and refactor
• [x] improve documentation of the functions

[johannesvollmer]

Hmmm maybe I shouldn't make spontaneous decisions at 3AM :D

Yes, I see your point. On the other hand, most people will have specified the dependency to exr = "1.5.6" or similar in their project. So running cargo update will bump that to anything <2.0.0 without asking, and then break their build if they do not use the absolutely newest Rust version. Is this expected behaviour? I thought it would be nice to explicitly opt-in to that, with more than just cargo update. However, I agree that splitting the ecosystem would not be good either.

[johannesvollmer]

I've opened #217 and would like to continue the discussion there, as it seems more appropriate. I yanked version 2.0.0 for now, which I released earlier at 3AM before going to bed, so I have might not put enough thought into it back then, whoopsie