Renamed List.foldPairs to List.foldPairwise and List.foldPairsBack to List.foldBackPairwise; this is so we use the same terminology as in the Seq.pairwise function.
Added documentation comments for IntSet (and TagSet) and IntMap (and TagMap).
Implemented Seq.replicate, Seq.repeat, and Seq.cycle, and stubbed unit tests for them.
Merge branch 'master' into vectors