Merge: lib: add `meta` as a user-level empty shell for meta-classes

Cleaning from old branches: a small useless meta-level.

The lib define meta-objects as some kind of multiton so you have a specific object to represent each class in the runtime-system (in fact each types because of genericity).

You can even define complex meta-deep hierarchy of meta-classes (with meta-loops).

The only issue is that these meta-objects are empty so basically useless (and meta-useless).

Pull-Request: #1205
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>