warnings: toggleable warnings

[hawkw]

Users should be able to turn individual warnings on and off, using the command line and/or possibly an eventual config file. I discussed this briefly in https://github.com/tokio-rs/console/issues/56#issuecomment-916256883.

Here's a rough summary of how I imagine this would work:

• [ ] Add a (reasonably) short, CLI-friendly name to lints.
  • This would probably be a short string name without spaces, something like self_wake_percent for the self-wake percentage lint.
  • We may also want to add numeric identifiers for lints.
  • This could be done by adding a function to the warnings::Warn trait returning an &'static str? It would unfortunately have to be a function rather than an associated const, since the Warn trait has to be object-safe.
• [ ] Store warnings in some kind of map from short names -> warnings.
  • One potential way to do this is using a compile-time hashmap like the phf crate.
• [ ] Add a CLI flag taking a list of lints to disable.
  • We may also want to add one that takes a list of lints to enable, in case we add lints that are not enabled by default
  • This would also be useful coupled with a --no-default-lints or similar.
• [ ] When the console starts, we would construct the list of lints based on the CLI arguments if they are provided.