Add chapter compilation support

[angerhang]

At the moment, we can only compile the whole thing from scratch which is not ideal as your source files increase. It would be good to use some package like subfiles to allow one compile each chapter individually.

[mcmanigle]

I agree this is a great idea. I don't have the free time right now to implement it, but happy to accept a merge request if one pops up, and/or will keep it on my list for when some free time arises.