Iter updates: make it similar to Java8 Stream.

Make Iter look like stream with common naming and signatures (where it makes sense).

Replace custom interfaces usage with Java8 java.util.* interfaces.

Add operation for iterators that have the coverage of Stream. This includes:

anyMatch
allMatch
noneMatch
findFirst -> Optional
findAny -> Optional
reduce(BinaryConsumer)
min(Comparator)
max(Comparator)
collect(Collector)