move common utils to helper.clj, move problem 001-010 to prob_001_010.clj
move problem 011-020 to prob_011_020.clj
move problem 021-030 to prob_021_030.clj
move problem 031-040 to prob_031_040.clj
move problem 041-050 to prob_041_050.clj
move problem 051-060 to prob_051_060.clj