nitg: intro the release option

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
android: use the release option to set type of compilation

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
Merge: Android release compilation mode

The --release option could also be used by pnacl.

Will need to specify usage in the Android and Nit manual. The resulting apk still needs to be signed and aligned before deployment.

Maybe add also suffix the package by ".debug". For now it can be done at the user level.

Pull-Request: #464
Reviewed-by: Jean Privat <jean@pryen.org>