RFC: Alternative codestyle document (see !2)

This is an alternative to the document proposed in !2 (closed). The document included here is based on a document I initial wrote myself for developing a linting tool for APKBUILDs.

Contrary to !2 (closed) it tries to document what most APKBUILDs, in my experience, already do. I figured that proposing a concrete alternative might be useful to streamline the styleguide discussion a bit, I am not saying the document proposed here is necessarily better. I also tried to keep the document as short and concise as possible.