In a contest, we know the scores of all our competitors, and we estimate that
our own score is equally likely to be any integer value between low and high,
inclusive. We want to know what our rank will most likely be. We define our
rank to be 1 + the number of competitors that beat us, so our rank will be
number 1 if no one beats us (even if several tie us).
Given a int scores, the scores of our competitors, and ints low and high, return our most likely rank. If there
is more than one most likely rank, return -1.