Remove huge m values from tests

Testing m values above 2^17 was asburd on such a small data set.
My words file only has 235886 elements.

Helpfully, this also highlights what is probably a bug since 7
of 13 m values are falling outside of their expected error range.
Five of the seven failing tests are off by at least an order of
magnitude.
Add Merge() method to combine two HyperLogLog instances