Make the API more generic/trait-aware

[UARTman]

Right now Hex API is written without much regard for traits. For example, it has multiple from_ methods that use the same code relying on From trait, as well as a from_str method that conflicts with the FromStr trait.

These can be either replaced or augmented with code that's generic over traits. This will make Hex a bit more capable and idiomatic.

Then, if making Hex more generic/trait-aware is a success, we can do the same to other types where necessary.

[yegor256]

@UARTman good point, let's do it

[yegor256]

@UARTman any progress here?

[UARTman]

@yegor256 Thanks for reminding me! I'll draft the PR with the changes I've been able to make so far today evening or tomorrow.

[UARTman]

@yegor256 I've done the first PR. However, there's still some ideas I'd like to look into, like a proper Into implementation and removing from_str_bytes and from_string_bytes entirely in favor of From<&str>.

[UARTman]

@yegor256 Most of the other code wasn't as obviously in need of trait implementations, since most of our types aren't thin wrappers over bytes. However, I'll take a closer look at whether there are places that will benefit from using slices or borrows.

Also, a question: should I implement more Froms for, say, i32 and f32 or will only i64, f64 and bool be stored?

[yegor256]

@UARTman yes, let's handle i32 and f32 too

[yegor256]

@UARTman what's up with this job, not yet complete?