Improvements

• #929: Convert 'flatMap'-Functions in 'io.jenetics.util.Streams' class into 'Gatherer'.
• #958: Replace home-grown hashing methods with calls to the JDK Objects.hash(...).

Bugs

• #960: Inconsistent calculation of EvolutionParamter.offspringSize().
• #962: Wrong Javadoc descriptions in Engine class.
• #964: Fix edge case in CompositeCodec.