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-cli.yaml

@@ -1,12 +1,19 @@
+mkdocs:
+  ## A directory to bring us from the mkdocs invocation directory to the gen-root
+  gen_root_dir: ..
+  site_dir: build_html
 make:
   id: cli
   target_name: CLIs
   target_suffix: -cli
   aggregated_target_suffix: -cli
   depends_on_suffix: ''
+  documentation_engine: mkdocs
   templates:
     - source: ../LICENSE.md
     - source: ../Cargo.toml
+    - source: mkdocs.yml
+    - source: README.md
     - source: main.rs
       output_dir: src
 cargo: