Clean up the implementation to take a uniform grid dataset as input
and splat using the correct world coordinates of the points into
the volume. Kernels are centred around the splat points in world coordinates
(floating point) and not quantized to the nearest voxel.
Skip the generation of all volume points which is unnecessary (memory usage).
Add ability to specify a radius array with one entry per splat point so
that the size of each splat may be controlled arbitrarily.
