Sampling chapter draft

I've been working on my chapter draft for the sampling application. It's not done, but I figured I would go ahead and submit a pull request in case anyone wanted to look at what I had so far. I have made (or am making) a few substantial changes:

* adding more emphasis on design decisions for programming for probabilities
* removing some of the emphasis on the specifics of rejection sampling
* including more examples of applications, and motivation for why you'd want to use this stuff

I'll be continuing to work on this today and tomorrow, and will make sure to post a comment indicating when I think it's ready for review.