Handicap Calculation: When we have more than 20 scores in the system, we calculate the index based on the best 8 of the last 20. For 3-20 scores we use a standard table
to determine how many scores to use and return the current handicap. For 3 scores, we also subtract 2 from the lowest score. For 4 or 6 scores, we subtract 1 from the average.