First draft of template engine chapter

I've added myself to the table of contributors, but I have a few questions about the information we're choosing to present.
Okay, this paragraph makes me think that the contents of the dict returned by `get_globals` will be a single function. You're saying here that it could contain any number of functions generated by the `CodeBuilder`, but we're limiting it to just the one for the same of simplicity. Is that right?

I think it would help to be a bit more explicit here.