v0.2.0

• add() now follows Algorithm 3's branching exactly (insert with probability
  p, remove otherwise) instead of an equivalent reformulation, cutting hash
  operations in half per element. Up to ~50% faster while the sample stays
  exact, ~7% faster once sub-sampling engages.
• Benchmark output and README tables now label results "faircount" instead of
  "CVM": the numbers measure this implementation, not the abstract algorithm.