Merge: Kill pseudo toplevel methods

Move some methods from Object to the top-level (Sys) as they do not rely on `self` and are intended to be called from everywhere.

Beside documentation improvement, this should slightly reduce the size of tables as methods introduced in Object are inherited by all classes.

Pull-Request: #1758
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>