Merge: Sys is top

And when I say *top* I mean *great*. But I also mean *top* in fact.

The idea is to move the top-level methods (those defined outside classes) from Object to Sys.
While this is a cosmetic move, it has a lot of benefits:

* top-level methods get a real meaningful receiver: the current system. It is meaningful both on the declaration side and the call side.
* no more need to distinguish the concept of top-level methods with their rules and semantic, so this simplify the language with one less thing (almost, see bellow)
* self is now usable in top-level methods, not that useful now because it is `sys`, a singleton, but this allow some kind of inheritance if you add super-classes to Sys.
* no more name conflicts between a standard class method and a top-level method
* no more useless slots in table of classes for crazy methods defined in Object and never redefined
* close #461 and close #1081 by making them irrelevant
* Let us see a bright future where the singleton Sys become a multiton and allow specific isolation of computation. Specific Sys will then be active objects (threads, computation node, actors, whatever) isolated with their own specific cloud of objects and efficient lock-less concurrency, dedicated memory model (realtime?), and why not transparent distribution

There is still two drawbacks

* what is the status of `sys` that represent the current `Sys`? I hard-coded it to stay a method in Object. One way to solve the probem is to make it a keyword (like `self`)
* when doing `foo(x)`, first this tries `self.foo(x)` then `sys.foo(x)` thus this is some additional rule of the language.

Pull-Request: #1249
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>