* Adding support for entity_id in EntityRuler pipeline component
* Adding Spacy Contributor aggreement
* Updating EntityRuler to use string.format instead of f strings
* Update Entity Ruler to support an 'id' attribute per pattern that explicitly identifies an entity.
* Fixing tests
* Remove custom extension entity_id and use built in ent_id token attribute.
* Changing entity_id to ent_id for consistent naming
* entity_ids => ent_ids
* Removing kb, cleaning up tests, making util functions private, use rsplit instead of split
<!--- Provide a general summary of your changes in the title. -->
## Description
* tidy up and adjust Cython code to code style
* improve docstrings and make calling `help()` nicer
* add URLs to new docs pages to docstrings wherever possible, mostly to user-facing objects
* fix various typos and inconsistencies in docs
### Types of change
enhancement, docs
## 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.
Kabir Khan