Moved methods from EKArrayStuff, EKSortStuff, EKSearchStuff into categories of NSArray and NSMutableArray. Updated main file

I started moving some methods (EKArrayStuff, EKSortStuff, EKSearchStuff) into appropriate NSArray and NSMutableArray categories. If you like the approach and the final outcome, I will do the same for EKStringStuff and EKNumberStuff.