Finished separating MLP calculations from image reconstruction.  Once the array defining the order on which histories enter image reconstruction, we perform the MLP calculations with this ordering and then writing this data to disk.  Once this is completed, image reconstruction can then begin without needing to perform MLP on each iteration by reading these paths back into memory one at a time.  Image reconstruction is now initiated by calling the function image_reconstruction which now contains functions and/or explicit code to calculate hull entry/exit coordinates, precalculate MLP paths, and iterative image reconstruction.