message: chore(api) improve documentation.
diff: @@ -948,6 +948,8 @@ mod inner {
  }
  }
  + // Implement `HostFunction` for a function that has the same arity than the tuple.
  + // This specific function has an environment.
  #[allow(unused_parens)]
  impl< $( $x, )* Rets, RetsAsResult, Env, Func >
  HostFunction<( $( $x ),* ), Rets, WithEnv, Env>
  