Npymath complex: support for complex in basic arithmetic: negative, add, subtract, multiply and the divides

If it was something more complex, I would look to use Structure, but for this particular case I think it is overkill. Since the point of using slots versus phi nodes is simplicity in coding, I don't think moving the two fields into an structure will help. I mean, in the same context programming in plain C, if needed I would go for separate variables instead of defining a struct. Just less boilerplate.