Confidence

----------------

- Enable referencing keys from values.
- Enable customizing load order for `load_name` through `loaders` and `Locality` (default behaviour remains unchanged).

------------------

- Warn about attribute access to configuration keys that collide with `Configuration` members.

----------------

- Enable escaping underscores in environment variables (`NAME_FOO__BAR` results in `config.foo_bar`).
- Use `yaml.safe_load` to avoid security issues with `yaml.load`.
- Raise `AttributeError` when attempting to set a non-protected attribute on a `Configuration` instance.

----------------

- Enable ignoring missing files in `loadf`.
- Fix crashes when reading empty or comment-only yaml files.

----------------

- Read files from [XDG-specified](https://specifications.freedesktop.org/basedir-spec/latest/) directories.
- Read files form system-wide and user-local directories specified in environment variables `PROGRAMDATA`, `APPDATA` and `LOCALAPPDATA` (in that order).
- Read files from `/Library/Preferences` and `~/Library/Preferences`.

------------------

- Expand user dirs for arguments to `loadf`, including values for `EXAMPLE_CONFIG_FILE` environment variables.