Initial refactorings and additions to support in-app config.
- Refactor our current options logic to support in-app configs. That is, we can write to a config file with our changes now.
- The default action when creating a new config file is to leave it blank. (TBD and for now, not sure on this one)
- Previously, we would set everything in a config file on startup; now we need to read from the config TOML struct whenever.
- `C` keybind is now occupied for configs.
- `no_write` option to never write to a config file.
Update dependencies to most recent versions if applicable. Refactor to deal with breaking changes. Drop MSRV due to dependency issues, just support stable and later.
