nitg-s: fix abstract methods in extern classes and add test

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg-s: fix call to super in primitive types and add test

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: fix conversion of hex char to int and add test

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>