feat: add blake3 160, 192 & 256 bits

[vlopes11]

closes #6

[bobbinth]

Thank you! Looks good! I left a few comments inline.

[bobbinth]

Looks good! Just one minor nit inline.

[0xkanekiken]

Looks good, thanks! I left a few very minor comments inline related to docs/comments.

[vlopes11]

@bobbinth I started a PR in winterfell fixing that. Unfortunately, it will not be an isolated change since it will impact also Hasher and ElementHasher (that will have to define their outputs).

Alternatively, we can wait for generic const expressions, so we don't leak the output requirement from the digest (hence, it can be defined during the trait implementation). Could be something like this in the end:

#![feature(generic_const_exprs)]

pub trait Digest {
    const OUTPUT: usize;

    fn as_bytes(&self) -> &[u8; Self::OUTPUT];
}

wdyt? If we go for the latter, then its an isolated change. The former, however, will require that all hasher defines their target output size (which kinda makes sense IMO, but it will change 3 traits instead of one)

[0xkanekiken]

Thanks! Looks good to me.

[Al-Kindi-0]

Looks good to me, and I am in favor of the generic const solution.

[bobbinth]

All looks good! Thank you!

Regarding Digest updates - I'd also prefer the const generic solution. So, let's wait for that.