Added a method to swap the value of two NSInteger pointers

I added a method to <code>EKNumberStuff</code>,  <code>+(void)swapValueOfIntPointer:(NSInteger *)xPointer withValueOfIntPointer:(NSInteger *)yPointer</code> to swap the value of two NSInteger pointers. Not sure if it's worth including in the library, but it shows an example of performing a swap without using a third variable.
I also updated the README file and the main.m so that it's including a run of the new method.