Added
NonEmptyIterator::group_by.NVec::sort_byandNEVec::sort_by_key.- An impl of
ExtendforNEVec.
Fixed
NEVec::sortavoids a second internalsort.
NonEmptyIterator::group_by.NVec::sort_by and NEVec::sort_by_key.Extend for NEVec.NEVec::sort avoids a second internal sort.