Added Population counts, enhancements for multiple-Redis backed filters

We needed to support multiple Redis-backed Bloom Filters, so I enhanced the logic to require providing a name for the filter. This also meant we needed to support a 'loadFilter' method, so that was added.

Finally we added a Population count feature to the filters. If an add() to the filter updates any bits (0->1) the population count is increased (for Redis filters the population is stored in Redis). Yes it is subject to the error rate on the filter, but for our needs that is okay. (This is different than a counting filter since we EXPECT the same key to be 'added' multiple times.)

This is VERY invasive, since the Redis value name needed to be passed around to support multiple filters.