Adds a translator to use Gettext on Android.

The implementation relies on a slightly modified version of
libintl-lite, release 0.5; a patched version of SDL 2 to add a
function returning the user's locale [1]. Moreover, the system
must have an implementation of fmemopen().

 [1] https://bugzilla.libsdl.org/show_bug.cgi?id=2131