New draft for the flow-shop chapter.

Latest changes according to feedback from @mdibernardo and a completed chapter draft.
Hi Christian, I really like this chapter. It's a useful approach to an interesting problem.

Your prose is nicely focused, and when you discuss a segment of code, you have the uncanny ability to insert a forward reference in the prose ("we'll get to this other thing later on") just as I'm thinking "oh, but what about..." :-)

I have a few suggestions that I'll add as line comments, but I think this chapter is looking very nice.