Move Max/Min from SGVector to CMath

@iglesias Agreed. I thought I would move them together when I move arg_max, max_abs, arg_max_abs. It would be faster and easier this way. I am moving the methods one-by-one because it would be easier to review and clean up as you mentioned. What do you think about me pushing all the commits here, moving individual methods with each commits and then you can merge after we have moved all the fuctions from SGVector to CMath?