Move blaze.{array,constructors} to blaze.objects.*
Split blaze.util into blaze.datashape.util and blaze.compute.util
Move blaze/playground to samples/playground.

This playground directory isn't very actively used, and the files don't
run presently, probably should delete it.
Move datadescriptor back to the top level

This one doesn't fit cleanly in io. Maybe it needs to be split up
as follows:

 - blaze.datadescriptor: interface, and memory data descriptor
 - blaze.io: data descriptors for files and other data IO
 - blaze.compute: deferred execution data descriptors
Merge pull request #95 from mwiebe/shuffle2

Second round of shuffling