This continues work started in
explosion/projects#147,
which provides features for automatically manipulating pipelines and
configs. The functions included are:

- merge: combine components from two pipelines and handle listeners
- use_transformer: use transformer as feature source
- use_tok2vec: use CNN tok2vec as feature source
- resume: make a version of a config for resuming training

Currently these are all grouped under a new `spacy configure` command.
That may not be the best place for them; in particular, `merge` may
belong elsewhere, since it outputs a pipeline rather than a config.

The current state of the PR is that the commands run, but there's only
one small test, and docs haven't been written yet. Docs can be started
but will depend somewhat on how the naming issues work out.

Maybe this will fix the CI issue?

This reverts commit be95ef5.

Adding the transformer component requires spacy-transformers, which
isn't present in the normal test env.

This also change the `output_file` arg to match other commands.

This removes one old print statement and some old TODOs. Some TODOs are
left as future work.

Co-authored-by: Raphael Mitsch <r.mitsch@outlook.com>