Update functional python

[smangham]

Decorators doesn't follow smoothly from the Lambdas -> Closures line.

We also don't really explain why decorators are useful or give any examples of them. A possible alternate format:

• Start with lambdas (e.g. minimum of list +1)
• What if we need to generate many similar lambdas -> function factory (minimum of list +N)
• What if we want to generalise our function factory -> function as argument (function of list +N)
• Function factories can be used to staple any behaviour onto a function transparently through decorators
  • Make small 'timing' decorator

This also ties into the issues with some people not realising the %% magic only works in the interpreter and asking for how you time things in scripts.

Also, in the academic class:

• People don't get __str__ and __repr__ - explain the differences or just remove __repr__
• Add short comments to each method explaining why they've been defined