using submodules

Is there a need to use submodules? The submodule concept is **quite** [tricky](https://github.com/progit/progit2/blob/master/book/07-git-tools/sections/submodules.asc), and this repo uses one submodule only. The contribution guide silently assumes a contributor masters the submodule concept.

E.g. when I want to contribute, I'll store my contributions on a branch that will be pushed and used for a pull request. But manipulating branches in the presence of submodules needs some experience (that I'm trying to acquire right now).

(see also e.g. https://codingkilledthecat.wordpress.com/2012/04/28/why-your-company-shouldnt-use-git-submodules/, but there are more examples out there)