Adding Text to Static Analysis Chapter

I've added the beginning (intro sections) of the chapter. I'm going to add 4 more sections, one for each of three "checks" that TypeCheck can make.

There probably needs to be more "this is how this works in Julia" notes added to the early code examples.
The most confusing part of this explanation was how you used the terms "function" and "method" as if the former is a collection of the latter. Does Julia's nomenclature use 'function' as "this is the mathematical concept of the function you are implementing" and method as "a method is one possible implementation of a function for a very specific set of typed arguments"? If so, I think this needs to be explained, because most of our readers will be accustomed to using those terms interchangeably.