* pytest file for issue4104 established
* edited default lookup english lemmatizer for spun; fixes issue 4102
* eliminated parameterization and sorted dictionary dependnency in issue 4104 test
* added contributor agreement
I wrote a small script to read the UD English training data and check
that our tag map and morph rules were resulting in the best POS map.
This hadn't been done for some time, and there have been various changes
to the UD schema since it has been done. After these changes we should
see much better agreement between our POS assignments and the UD POS
tags.
<!--- Provide a general summary of your changes in the title. -->
## Description
- [x] Use [`black`](https://github.com/ambv/black) to auto-format all `.py` files.
- [x] Update flake8 config to exclude very large files (lemmatization tables etc.)
- [x] Update code to be compatible with flake8 rules
- [x] Fix various small bugs, inconsistencies and messy stuff in the language data
- [x] Update docs to explain new code style (`black`, `flake8`, when to use `# fmt: off` and `# fmt: on` and what `# noqa` means)
Once #2932 is merged, which auto-formats and tidies up the CLI, we'll be able to run `flake8 spacy` actually get meaningful results.
At the moment, the code style and linting isn't applied automatically, but I'm hoping that the new [GitHub Actions](https://github.com/features/actions) will let us auto-format pull requests and post comments with relevant linting information.
### Types of change
enhancement, code style
## Checklist
<!--- Before you submit the PR, go over this checklist and make sure you can
tick off all the boxes. [] -> [x] -->
- [x] I have submitted the spaCy Contributor Agreement.
- [x] I ran the tests, and all new and existing tests passed.
- [x] My changes don't require a change to the documentation, or if they do, I've added all required information.
Renaming the tag with an underscore lets us add it to the tag map
without worrying that we'll change the sequence of tags, which throws
off the tag-to-ID mapping. For instance, if we inserted a 'SP' tag,
the "VERB" tag is pushed to a different class ID, and the model is all
messed up.
