Merge pull request #439 from mrocklin/numpy

compute: add numpy backend
Speed up import by turning off multipledispatch ordering

See https://github.com/mrocklin/multipledispatch/pull/29

This significantly speeds up import time.  Dispatch import time used to
dominate (4s if using all backends) now it's a small fraction of a second.
Merge pull request #442 from mrocklin/fast-import

Speed up import by turning off multipledispatch ordering
Merge branch 'master' into bcolz