How to add a menu item to main menu: hook_menu() or menu_link_save()?
After a hard time I figured out what hampered the execution of the above code: clearing caches isn't enough to see the results. I had to use devels menu reset (/devel/menu/reset). Using drush's drush eval 'menu_rebuild();' as mentioned at How do I call the menu_rebuild function in Drupal 7? somehow does not work. I do not know why.