Also add some docstrings and questions

I spotted a neat way of doing this before I had to head off so couldn't resist

Exercise 5 requries stdin so we will come abck to that once I figure out how
best to do that.

Primes generation could be more efficient.

Skips labs 1-3, did them in eclipse which failed to save to OneDrive (!)

Implements Lab and Section classes for more easily and consistently running
particular labs.