Add option verbosity and modernize repository

[keurfonluu]

• Added: option verbosity to control the amount of outputs as a fraction of population size when return_all = True.

Reminders:

• [x] Run invoke format to make sure the code follows the style guide,
• [x] Add tests for new features or tests that would have caught the bug that you're fixing,
• [x] Write detailed docstrings for all functions, classes and/or methods,
• [x] If adding new functionality, unit test it and add it to the documentation.