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 --combined tests/niti.skip
index f9489e3,394cdeb..7c2762c
--- 1/tests/niti.skip
--- 2/tests/niti.skip
+++ b/tests/niti.skip
@@@ -6,8 -6,6 +6,8 @@@ shoot_logi
  bench_
  nit_args1
  nit_args3
 +nitvm_args1
 +nitvm_args3
  nitc_args1
  nitg_args1
  nitg_args3
@@@ -19,3 -17,4 +19,4 @@@ test_android_platfor
  android
  nitcc_parser_gen
  mnit
+ emscripten