Repository maintenance

[bbonenfant]

Upon making the repository public, Github and PyPI advised to change a few things about the repository:

• Moved the CODE_OF_CONDUCT.md to the project root.
• Organized the CLA to make it more understandable to straight-forward to sign.
• Started the CHANGELOG.md
• Added workflow that builds and publishes the package to PyPI when a *.*.* tag is pushed to the primary branch.
• Updated the CONTRIBUTING.md to document the branching guidelines.
• Added more metadata to the pyproject.toml file (and fixed some dependencies).