bitstring-4.0.2

A maintenance release.

• Added py.typed file and converted the module to a package to let mypy find type
  annotations. Bug 248.
• Fix to shifting operations when using LSB0 mode. Bug 251.
• A few more fixes for LSB0 mode.
• Improved LSB0 documentation.
• Added build-system section to pyproject.toml. Bug 243.
• Rewrote the walkthrough documentation as a jupyter notebook.
• Updated the project's logo.