RaCoCo result: Red::AST::Constraints

# Red::AST::Constraints 50%

    use Red::AST;
    use Red::Column;

    class Red::AST::Constraint does Red::AST {
        has Red::Column @.columns;

        method returns { Nil }
        method args { |@!columns }
        method find-column-name {}
    }

    #| Represents an unique constraint
    class Red::AST::Unique is Red::AST::Constraint {}
    #| Represents a primary key constraint
    class Red::AST::Pk     is Red::AST::Constraint {}