Check spelling with `hunspell` and/or `nlprule`.

Use Cases:

Run `cargo spellcheck --fix` or `cargo spellcheck fix` to fix all your
documentation comments in order to avoid nasty typos all over your source tree.
Meant as a helper simplifying review as well as improving CI checks after a
learning phase for custom/topic specific lingo.

`cargo-spellcheck` is also a valuable tool to run from git commit hooks or CI/CD
systems.

Examples of use:

Check for spelling and/or grammar mistakes:
$ cargo spellcheck check

Apply suggestions interactively:
$ cargo spellcheck fix