v0.3.0

• Avoid iterating over empty bins when using Stores's methods (getStream, getAscendingStream, getDescendingStream, getAscendingIterator and getDescendingIterator)
• Track bin counts as double and update the signature of related methods

This release introduces breaking API changes:

• QuantileSketch.getCount(), Store.getTotalCount() and Bin.getCount() now return a double instead of a long,
• Store has a new add method with signature void add(int, double),
• the constructor of Bin now takes a double as a second parameter (count).