Add several ensemblist methods to BloomFilter

Based on https://en.wikipedia.org/wiki/Bloom_filter#The_union_and_intersection_of_sets

I didn’t find any references on the precision of those operations in Swamidass & Baldi (2007),
so I assumed a 1% error margin during the tests.

- approxCount()
- approxInterSize()
- approxUnionSize()

This one is not an approximation:

- union()