Clarify SweepstakesAssignment.AVERAGE and add AVERAGE_ALL
Add Sweepstakes and assignPoints

This class handles figuring out sweepstakes totals. It takes simply the
number of people in each place and skips places when needed--so, a
two-way tie for first followed by a third place competitor would be
passed into quantities as {2, 1}.
Document Sweepstakes.assignPoints