Optimized the distribution of default user IDs

If a "key" isn't specified for a user account, then we can just randomly
assign the user account to a test bucket without resorting to hashing
functions.

However, since our default hashing function is pretty simple, we
document ways to use other routines.
Experiment show-casing default hashing function

Our hashing function (that we use to split users into test buckets based
on keys that might be similar to GUIDs) is pretty simplistic. But the
goal of uniform distribution may or may not work well.

In this experiment, we create thousands of GUIDs and use our hashing
function as well as a Murmur Hash function and graphically show how they
compare.