bcolz: use python streaming in cheap head case
bcolz: respects keepdims
numpy: count respects keepdims
numpy: nunique keepdims
split: recipe for nunique
bcolz: use into(Iterator, data), not iter(data)
numpy: fix bugs around use of ndim for axis checking
bcolz: swap path arguments
mongo: nunique
Merge pull request #823 from mrocklin/bcolz-head-faster

Various improvements to support fbp