Rewrite cli.py to use Click and finalize public API

[stefanooldeman]

Use Click and rewriting pyrandall/cli.py to improve code readability before we add extra features / commands.

This change MUST bump the major in VERSION to allow us:

• to deprecate the sanitycheck command.
• to change naming and position of optional args and positional args

When rewriting the cli.py, also consider improving the tests in tests/functional. Either by calling pyrandall commands with subprocess.Popen. Or a different approach that is commonly practiced to test Click (command line interfaces).

[stefanooldeman]

Low hanging fruit, might pick this up next to get the cli interface to a stable state.