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.
I think the conclusion might be expanded on some, it feels like an abrupt end to what is otherwise a well paced chapter. Possibly address other means of static analysis outside of:

    How do we find loops?
    How do we find variables in loops?
    How do we find the types of a variable?
    How do we print the results?
    How do we tell if the type is unstable?

There's no need to explain the methods of analysis but more of a "you might also consider the following..." or similar.