Implement __repr__ magic for common classes

[brews]

Implementing __repr__ magic methods for our most commonly used classes would help error output and debugging.

Printing objects or having them dumped in a traceback gives us a class name and a memory address. It would save ssssoooo much time to get more info in this output. Ideally we could quickly fix this by implementing __repr__ methods and having it print out class names and instantiating parameters. So a RollingCalculation instance (made up example) prints as RollingCalculation(method="median", window_size=30).

Suggest implementing __repr__ because this is also the fallback for __str__ magic, too. Too birds with one stone.