Update on peer review

Because so many students requested extensions for assignment 4 and peer review assignments can't go out until the assignments are turned in, we've delayed the due date for peer review for everyone to next Friday, 22. October, effectively granting everyone a 7-day extension on this one assignment. We don't intend this to impact following deadlines, but we'll keep track of how students are doing.

This and all future peer reviews should be a small assignment - a few hours at most. We are not asking you to fix every problem you can find, only to find something to improve for each exercise (4.1-4.4), such as fixing a bug, improving docstrings or error handling, or adding a test if everything already looks great. Implementing some missing functionality is certainly an appropriate improvement, but definitely not all if there are big gaps or problems. The goal is to exercise learning from each other by critically reading someone else's code.