New draft for the flow-shop chapter.

Latest changes according to feedback from @mdibernardo and a completed chapter draft.
I tripped over this formal problem definition a little bit. I'm not always the best at parsing things like this, and tend to grok a bit faster if there's an accompanying example. You do this later on, and I think your diagrams are great. Maybe adding a small, concrete example would help, such as a job that consists of two or three tasks on a car assembly line.

Or, I think some small changes to the variable naming might help - could it be "m machines and n jobs"?