v1.2.2

• Added teeing collector (from Java 12)
• Added mapMulti operator for all streams and mapMultiToInt, mapMultiToLong, mapMultiToDouble to object Stream (from Java 16)
• Added findFirstOrElse(defaultValue), append(T), prepend(T) to Stream (thanks to @wjtxyz)
• concat now supports 3+ streams or iterators
• Added SpinedBuffer for objects. SpinedBuffer now public, but it slightly differs from Java 8 API.
• Fixed unnecessary unboxing of dropWhile, takeUntil, filterIndexed, mapIndexed and scan operators in primitive streams
• Methods marked with nullability annotations
• Many other improvements