Nb-clean

This minor release adds optional functionality to preserve cell metadata. The `configure-git`, `clean`, and `check` subcommands now support an optional `-m`/`--preserve-metadata` flag. When this is set, `nb-clean configure-git` and `nb-clean clean` won't remove cell metadata from notebooks, and `nb-clean check` won't fail if the notebook contains cell metadata.

This minor release adds optional functionality to remove empty cells. The `configure-git`, `clean`, and `check` subcommands now support an optional `-e`/`--remove-empty` flag. When this is set, `nb-clean configure-git` and `nb-clean clean` will remove empty cells from notebooks in addition to removing cell execution counts, metadata, and outputs, and `nb-clean check` will fail if the notebook contains empty cells.

This patch release fixes an incorrect error message when calling `nb-clean unconfigure-git` in a Git repository which did not have the `nb-clean` filter installed. Previously, it would be reported that the working directory was not a Git repository. Now it's correctly reported that an `nb-clean` section is not present in the repository's Git configuration file.

This patch release unpins the dependency on `nbformat` to allow installation alongside recent releases of Jupyter.

This patch release fixes some inconsistent terminology in docstrings and strings printed by the `check` subcommand.

This minor release adds a `check` subcommand that determines if a notebook is clean or not, which can be used as a check in your continuous integration pipelines.