Merge: Compilation to JavaScript using the Emscripten SDK

Published for review but still needs some doc and examples. Works with most small examples but not yet with the naive_interpreter (but it's not clear why).

Usage:

    apt-get emscripten
    nitg -m emscripten examples/hello_world.nit
    nodejs hello_wold.js

Pull-Request: #506
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>

diff --cc tests/niti.skip
Simple merge