A complete re-write of the cubic interpolation code.

The key change is that there is a new layer of abstract,
a Array object that the interpolator depends on.

The Array provides a one dimension or two dimensional
array like interface independent of the underlying representation
of the data.

Also included here is support for vector valued functions.

Change-Id: Ica68f03778cf0d84192db00cd55653f8b4124d51