some slight re-organization

I'm curious if I should just go for broke and attempt at least functions
in this lecture.

In that way I can have to students work on some more interesting
problems.
moving slides around

* I had some numpy in lecture2 that is now in lecture5
* I've got lectures 2 and 3 a little closer to the outline
added if, while and another example

By adding even a basic introduction to functions in the first lecture I
think we can provide a more challenging set of problems for the students
to practice.