Every class and method gets a thorough, helpful docstring

Nova is under-commented. It is missing docstrings on many classes, methods, and functions. The docstrings it has are often not helpful. This impedes understanding of the code and slows development. With few exceptions, Nova's docstrings should include thorough explanations, and arg descriptions, and sometimes example usage. Long or unclear sections of code should have explanatory comments to guide the reader. Docstring existence should be enforced with pylint; good docstrings and good commenting practices should be encouraged through code review.