Fix docs coverage and add tests coverage workflow check

[khiga8]

Fixes #25
Fixes #24

This fixes the docs coverage workflow which is currently broken.
This also introduces a test coverage workflow to ensure that there is a test for each rule.

You can also run the following locally to check coverage:

bundle exec rake docs:coverage
bundle exec rake tests:coverage

[khiga8]

test coverage check demonstrates the missing test coverage check.

docs coverage check demonstrates the missing docs coverage check.

[lindseywild]

🎉