settle on a docstring format and update all docstrings #427

As discussed in #425.

Suggest using the numpy format, and integrating pydocstyle into test framework

TODO:

• Update constraint.py Update docs & linting for constraints.py, target_space.py #440
• Update logger.py Replace custom colour implementation, add docs for logger.py, util.py #435
• Update util.py Replace custom colour implementation, add docs for logger.py, util.py #435
• Update domain_reduction.py bounds_transformer could bypass global_bounds due to the test logic within _trim function in domain_reduction.py #441
• Update observer.py Update various docstrings, add workflow to check docstrings #445
• Update bayesian_optimization.pyUpdate various docstrings, add workflow to check docstrings #445
• Update event.py Update various docstrings, add workflow to check docstrings #445
• Update target_space.py Update docs & linting for constraints.py, target_space.py #440
• Integrate pydocstyle into testing. Update various docstrings, add workflow to check docstrings #445
• Use numpydoc