Dense primitive arrays where the lower index is zero (or the equivalent of zero for newtypes and enumerations).

Actual writes to data structures use a more safe write instead of the unsafe unsafeWrite. Writes also tend to occur much less in DP algorithms (say, N^2 writes for an N^3 time algorithm -- mostly reads are being executed).

TODO consider if we want to force the lower index to be zero, or allow non-zero lower indices. Will have to be considered together with the Index.Class module!

TODO while Unboxed is, in princile, Hashable, we'd need the corresponding VU.Vector instances ...