Add blake3 and blake3_file hash functions

[tgross35]

Blake3 is a hash algorithm that is pretty popular when working with larger files, and is also (in theory) closer to SHA-3 in security than SHA-2. I believe it is used by sccache and some other larger build systems.

This adds blake3 and blake3_file functions. blake3_file is especially of note because it uses mmap and parallelization rather than reading the file into memory, so it should outperform sha256_file quite a bit (this is the same function used by the b3sum utility).

I need to rebase since I did this a while ago, but I may as well get your thoughts here.

[casey]

Love it, this is super cool.

[tgross35]

Awesome! I rebased so this should be all set for a look.

[casey]

Nice, LGTM! I used blake3::hash instead of a hasher in in blake3(), since it's one and done and doesn't need incremental updates. I also changed uses of path.to_str to path.display(). Since paths are arbitrary bytes, they can't necessarily be converted to a string, and path.display returns something that represents a path but has a display implementation, so it can be printed. It looks like we made the same mistake in the sha256 functions, so I fixed those too.

[casey]

I also added <sup>master</sup> annotations, so people know this hasn't made it into a release yet.

[tgross35]

Awesome, thanks!