* Move utils out of the entry points module and move the rose-stem entry
  point in.
* Move fileinstall into its own module.
* Sort imports.

* `['a'].sort()` returns `None` not `['a']`
* So `assert a.sort() == b.sort()` will always be `True`.

* Avoid having to handle None values for srcdir/rundir throughout
  the codebase by catching them earlier.

* A future rose stem interface will need to inject itself
  between config loading and processing.
* So colocate the plugin processing logic into one function.

* Entry points accept missing or None values for arguments, however,
  this can never happen in practice.
* Set the appropriate type hints and remove code paths which could not
  get executed.

* Amend false docstrings.
* Rename a couple of modules.