Final version of my cube patch - fixed test cases, added documentation

Any committers want to take ownership of this?

Thanks,

Joshua Reich

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Changes that were made in July 2006 by Joshua Reich I.

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Code Cleanup:

Update the calling convention for all external facing functions. By
external
facing, I mean all functions that are directly referenced in cube.sql.
Prior
to my update, all functions used the older V0 calling convention. They now
use V1.

New Functions:

cube(float[]), which makes a zero volume cube from a float array

cube(float[], float[]), which allows the user to create a cube from
two float arrays; one for the upper right and one for the lower left
coordinate.

cube_subset(cube, int4[]), to allow you to reorder or choose a subset of
dimensions from a cube, using index values specified in the array.