Allowing includes to require other named includes

This changes specifically addresses my requirements as mentioned in #382 

Unfortunately, I was not able to find a way to cleanly parse included files as thoroughly as others, so it's pretty limited in that it can only include other named requires. Thus, it works for me, since I only needed to provide a `path` include.

This is enough to satisfy all the plugin use-cases I've considered so far, but it could be a limitation that we want to address in the future if the need arises.