Extras for Java 8+ Streams

This provides some extra collectors to use with Java 8+ streams.

The collectors provided are:

1. RandomValueCollector - returns one random value from from the stream. Each item has an equal probability of being returned. If the stream is empty, Optional.empty() is returned.

2. TopNCollector - returns the top N values in the stream. If the stream contains fewer than N items, the entire stream is returned. The stream value type must implement the Comparable interface.

Code Examples

 // collect one value from the stream where each value has equal
 // probability of being chosen
 IntStream.range(1, 20).boxed().collect(new RandomValueCollector())

 // collect only the top 5 values using the objects natural ordering
 IntStream.range(1, 20).boxed().collect(new TopNCollector(5))