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
Escape_to_c fesait pas l'affaire... Je crois que la fonction C fait des escape, mais je ne sais pas exactement sur quoi. Mais il faudra faire plus
 de debuggage!