feat(hub): generate hub implementation and docs

This includes docs for the library usage.
It's totally great to be able to paste example code right were it
belongs, and also put the same elsewhere to compose more complex docs.

src/rust/cmn.rs

@@ -1,5 +1,10 @@
 use std::marker::MarkerTrait;
 
+/// Identifies the Hub. There is only one per library, this trait is supposed
+/// to make intended use more explicit.
+/// The hub allows to access all resource methods more easily.
+pub trait Hub: MarkerTrait {}
+
 /// Identifies types which can be inserted and deleted.
 /// Types with this trait are most commonly used by clients of this API.
 pub trait Resource: MarkerTrait {}