The workspace root path is a base path for bundle storage. If not
specified, it defaults to `~/.bundle/name/environment`. This default, or
other paths starting with `~` are expanded to the current user's home
directory. The configuration also includes fields for the files path,
artifacts path, and state path. By default, these are nested under the
root path, but can be overridden if needed.
This adds:
* Top level "artifacts" configuration key
* Support for notebooks (does language detection and upload)
* Merge of per-environment artifacts (or artifact overrides) into top level
Load a tree of configuration files anchored at `bundle.yml` into the
`config.Root` struct.
All mutations (from setting defaults to merging files) are observable
through the `mutator.Mutator` interface.
shreyas-goenka
Pieter Noordhuis