Added helpers for handling primitive values at the end of null-safe navigation chains

Increased minimum Xtend version to 2.15, mainly due to build issues

Bumped Xtend minimum version to 2.13

Added combinations and combinationsWith extension methods for Iterator and Iterable to generate cartesian products.

Added withoutAll extension methods for Iterable and Iterator to filter elements from the source available in another Iterable.

Added partitionBy extension methods for Iterator and Iterable, partitioning elements into two aggregates: selected and rejected.

Added Iterator/Iterable extension methods groupIntoListBy and groupIntoSetBy to group elements by given classes.

Added into extension methods to Iterator/Iterable to add elements to one or more Collections.

Added summarize extension methods for PrimitiveIterators to compute count, min, max, average and sum of provided values.

Added streamRemainingExhaustive extension method for PrimitiveIterators that is guaranteed to pull elements from the originating iterator.

Functional factory methods for and in LongIterable and DoubleIterable.

Added mapOrGet extension method for Optional.

Added forEach method for object arrays to iterate over elements without instantiation of an iterator.

Extension methods for Optionals

Extension methods for Xtend IntegerRanges

Extension methods for primitive arrays

Extension methods for Java Streams

Extension methods for Iterables

Extension methods for Java Strings

Extension methods for Java Durations

Extension methods for Xtend functions

Extension methods for Java CompletableFutures

Scheduling utilities

Asynchronous execution utilities

Primitive Iterables