partitions: test uneven chunk sizes
compute: compute passes kwargs through to compute_up/down
partition: flatten recurses
partitions returns flattened iterator
h5py: uses flattened partitions function
interativity: compute(expr) accepts kwargs
expr: slice operation no longer defines repr
expr: function to compute shape of aggregate
split: reasons correctly about uneven chunk sizes

cc @mwiebe
h5py: test computation on uneven chunk sizes