Implement FromHex for 32-byte arrays

[illicitonion]

No description provided.

[LukasKalbertodt]

Hello and thanks for your PR! Adding one specific array length begs the question: why not other lengths? We could, for example, add all multiple of 8 below or equal to 64 (24, 32, 40, 48, 56, 64). I'm not sure what's the right solution here. Any other opinions?

[illicitonion]

I'm happy to add multiples of 8 up to some value, I just had a need for 32 because it's a pretty common digest algorithm output size (and one I'm using).

Longer-term, I think rust-lang/rust#44580 means we should be able to make this generic in the future (its RFC got accepted, and someone is interested in working on it).

[LukasKalbertodt]

Yip, absolutely, the current situation is just a dirty hack. Anyway, I'm not the maintainer of this crate, so you' (we) will have to wait for @KokaKiwi to decide what numbers to add ^_^

[KokaKiwi]

Hi, long time I haven't been active here (kind of a chaotic schedule recently, in my head too ^^")
I think of adding some sizes to implement, but that's purely arbitrary at the moment (as Lukas said, that's just dirty hack in waiting for the RFC): 24, 48 and 64 (multiples of 16 between 16 and 64 seemed to be a good thing to me)

[illicitonion]

Done :) Thanks!