nitg/ffi: move most FFI services from AModule to MModule

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg-g: test use of java FFI across many modules

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg/ffi: mark as private methods internal to compiler_ffi

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
ffi/java: callbacks are relative to mainmodule

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
ffi/java: use C callbacks instead of going straight to nitni (for global)

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
ffi: minor clean up

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
android: support use of -m

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
ffi: fix support for generated calls with generic types (for Java FFI)

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Merge: Refactor FFI, the framework is now based on MModules

* Should fix #437 by supporting the use of the Java FFI across many modules in global compilation.
* Should also work (but we need an example for it): `nitg cross_platform_prog.nit -m android`

Pull-Request: #456
Reviewed-by: Jean Privat <jean@pryen.org>