Publish a proper pip package for clippy-kindle

[dangbert]

Should make it much easier for people to install and use this repo (e.g. pip install clippy-kindle)

References:

• tutorial: Packaging Python projects
• tutorial2
• tutorial3

Considerations:

• ensure pytest and docs dependencies are not required for installing this pip package. (need a better way to manage dev vs prod dependencies)

• usetox for testing/validation of package in future