Add case-conversion functions (#1376)

[gVirtu]

As per #1376, adds a thin wrapper to heck's case conversion utilities, along with straightforward tests to each one.

Hopefully it ends up being useful! :)

[casey]

Very nice! To make it super obvious what the different functions do, let's use the destination case in the description of each function.

[casey]

I went ahead and committed the suggested changes to the readme.

[casey]

FYI, since just is a binary crate, changes to Cargo.lock should be committed.

Merged, thank you for the PR! I'm sure people will wind up using this. Case conversion is common enough, and case conversion in the shell is pretty miserable.

[gVirtu]

@casey thank you!! I'd signed off for the day so appreciate the help.

I wasn't sure about the Cargo.lock change (newbie to the rust ecosystem 😃 ) since heck ended up being the only one with a version number so I suspected it was a Rust version mismatch on my end.

Thank you once more and congratulations on maintaining the project, it's organized very nicely, easy to set up and well tested. I'm starring it myself!

[casey]

You bet, and thank you for the kind words! Contributions like yours make it fun and motivating to work on in the long term, so thank you!