[docs] revamp bitmask dev docs

AUTHORS

Makefile

NEWS

docs/authors.rst

docs/bonafide/index.rst

docs/changelog-next.rst

docs/changelog.rst

docs/cli/index.rst

docs/conf.py

docs/core/core_api_contract

docs/core/index.rst

docs/designdocs/index.rst

docs/hacking/index.rst

docs/hacking/release.rst

docs/hooks/leap-autopep8.post-commit.hook

docs/hooks/leap-autopep8.post-commit.hook.ADD

docs/hooks/leap-commit-template

docs/hooks/leap-commit-template.README

docs/hooks/leap-flake8.pre-commit.hook

docs/index.rst