feat(make): cli depends on API, generically

This allows us to build efficiently. CLI programs can now have their
own cmn.rs implementation, which we can test standalone with
`cargo test`.

The primary makefile currently just explicitly pulls in the type-*.yaml,
one day we could possibly put it into a loop.

Fixes #11

gen/groupsmigration1-cli/src/cmn.rs

@@ -0,0 +1,2 @@
+// COPY OF 'src/rust/cli/cmn.rs'
+// DO NOT EDIT

gen/groupsmigration1-cli/src/main.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, groupsmigration:v1 !");
+}