Given three parameters, a, b and c, return the sum of the numbers between a and b (inclusive) skipping by c. (c will always be greater than 0) Note: a might be greater than, less than, or even equal to b! For example: sumABSkipC(1,5,1) would count from 1 to 5 by 1, counting 1, 2, 3, 4, 5, resulting in the sum 1+2+3+4+5=15. sumABSkipC(1,5,2) would count from 1 to 5 by 2, counting 1, 3, 5 resulting in the sum 1+3+5=9. sumABSkipC(9,-3,3) would count from 9 to -3 by 3, counting 9, 6, 3, 0, -3 resulting in the sum 9+6+3+0+-3=15.