Support loading configuration from .config/helix in project directory

[dbowring]

In addition to <project>/.helix, also try to load configuration from <project>/.config/helix.

This is not ready to merge, some pending discussions/choices:

• Is this worth supporting?
• What should the behavior be if both directories have a config.toml or a ignore?, E.g., .helix/config.toml and .config/helix/config.toml
• What should the behavior be if config.toml is present in one and ignore in the other? E.g., .helix/config.toml and .config/helix/ignore.

I like using the .config directory with the tools that currently support it to avoid having lots of dotfiles in the repo root, but this is not (yet?) widespread.

Would this be something you would be willing to support? I'm not particularly experienced with rust but I'd be interested in giving an implementation a shot pending answers to the above questions.