IDEAS

get callback from partitioning working again!

also 1 bit/hash table entry, for basic partitioning?  (REDUCE MEM USAGE/FP)

replace memory structures for map, set to be cheaper; see Matt Austern's
  treatise.

run velvet??

probably want to randomize which group files different partitions go into...?

TODO in the future
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put locks around the I/O functions.