feat(mkdocs): mkdocs generator works now

It can be selected for each type of program we want to build, and makes
sense for everything that is not a library.

We also tried to unify names and folders a bit more, even though there
certainly is more work to be done to be fully non-redundant.

Fixes #43

etc/api/type-api.yaml

@@ -17,6 +17,7 @@ make:
   aggregated_target_suffix: -api
   depends_on_suffix:
   global_targets: Yes
+  documentation_engine: rustdoc
   templates:
     # all output directories are relative to the one set for the respective API
     - source: README.md