Expose CKMS point counts (#5)
Expose CKMS point counts (#5)

This commit exposes the total number of points seen by a CKMS
datastructure through a function called `count()`. This removes
the need for the client to compute and store this information.

Signed-off-by: Brian L. Troutwine <ccec23efb0a0e18dff61cc3fd9b4cf2532883527@postmates.com>
cmsd2/quantiles,postmates/quantiles