Remove unused fields
Implement QuantileDigest merging
Add method to dump quantile digest as a graphviz tree
Move thread-safety from QuantileDigest to Distribution
Serialize/deserialize quantile digest
Fix boundary conditions
Only compress if sum(weights) < floor(n/k)

This was inadvertently broken when we implemented exponential decay and make weightedCount a double instead of a long
Don't throw IOException in QuantileDigest serialize/deserialize
Add method to estimate in-memory size of QuantileDigest
Handle the full range of long values in quantile digest
Formatting
Memoize size of QuantileDigest and Node classes to avoid walking their structure every time