add support for inlining partials

This allows optional (and opt-in) inlining of partials. It injects the parsed AST of partials in place of the traditional `partial` nodes, which cause `registerPartial` calls in the compiled templates. The rational is that this is sometimes more convenient in contexts such as AMD and Require.js, when you are compiling each template independently, and it can become tedious to ensure you require all partial dependencies of a template whenever you require the template itself in a module.

Feedback and suggestions are welcome. There is nothing special about this implementation, I'm just throwing the idea out there.