Added x5__with_prec.
Added module rankin_cohen_diff.
Modified _rankin_cohen_bracket_func.
Modified _down_prec.
Added rankin_cohen_pair_x5 and rankin_cohen_triple_x5.
Fixed _rankin_cohen_bracket_func.
Modified rankin_cohen_pair_x5.
Added m_operator.
Modified rankin_cohen_triple_x5.
Added a test for rankin_cohen_triple_x5.
Refactoring.