Deserialize into a fixed-size array

[dtolnay]

Feedback from shssoichiro/avsser#2 (comment):

I will say I wish that the hex crate could deserialize into a fixed-size array, like rustc-serialize could. I found a better way to do it in this crate (because the hex strings were UUIDs), but it would still be a good functionality to have.

[LukasKalbertodt]

Added in #11 (for arrays up to size 16, but that can easily be extended)

[zrkn]

Any plans for releasing it to crates.io?

[KokaKiwi]

I'm thinking about publishing a 0.3.0 version in crates.io with the current changes, and publishing a 0.3.1 with #13, which seems to me to be a sufficiently good way to do this thing

[KokaKiwi]

I published a 0.3.0 version with latest changes (minus #13), so I'm closing this issue