Add "staticMethod" helper and update static functions to use it.
Improve detection of Symbol.iterator and fix getIterator.
Implement pluck, invoke, unique, and find.
Implement product.
Update Symbol.iterator comments.
Implement chunk.
Generalize zip and implement zipLongest.
Add isIterable helper and implement flatten.
Implement tee.
Implement unzip.
Implement ireduce.
Merge remote-tracking branch 'fitzgen/es6-impls' into es6
Remove combinatoric methods, s/ireduce/reductions/, little fixups
items is assigned to so it can't be const