interface.pyx: function_index -> problem_index and docstrings improved
interface.pyx: function_index -> problem_index and docstrings improved

NDManh/numbbo,dtusar/coco,NDManh/numbbo,dtusar/coco,dtusar/coco,oaelhara/numbbo,NDManh/numbbo,NDManh/numbbo,dtusar/coco,oaelhara/numbbo,oaelhara/numbbo,NDManh/numbbo,oaelhara/numbbo,oaelhara/numbbo,oaelhara/numbbo,oaelhara/numbbo,oaelhara/numbbo,NDManh/numbbo,NDManh/numbbo,NDManh/numbbo,dtusar/coco,dtusar/coco,dtusar/coco,dtusar/coco,dtusar/coco,oaelhara/numbbo,NDManh/numbbo