Fixed distance function for Cartesian data - bug.
witched validation code wholesale over to DataArray using getrow method.
Added plotting function for SEPP validation data.  TODO: add more plots, at the moment it's just SER.
Added to implementation code for Chicago - trying to get a handle on the effect of grid size.
Added code to cad module for using Monsuru's method.  TODO: test the old apply_point_process, does it still work with the new abstraction?