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.
I'm finding keeping track of these multiple contexts a little hard. It seems like there are (at least) two contexts: at least one for the `Templite` which defines things such as the filters available for processing template variables, and one for the `CodeBuilder`(s) which defines the template variables themselves. Is that right? I'm not sure how to make it more clear, since they *are* both contexts. Maybe they could have different names or something?