nitvm: Keep the positions of method and attribute blocks in each class and fixing a bad allocation of internal structures for attributes

Signed-off-by: Julien Pagès <julien.projet@gmail.com>
nitvm: Introduce a custom algorithm for ordering superclasses

Signed-off-by: Julien Pagès <julien.projet@gmail.com>
nitvm: Fixe a bad allocation of the internal structures of attributes

Signed-off-by: Julien Pagès <julien.projet@gmail.com>