Finished refactor for groups. Plotting by patch now so that the output of slice_faceted_model can be printed the same way despite the input args.
Changed the -g flag to --by-groups
Added lineweight and alpha setting to patches.
Fixed problem with mismatched group names. If no intersections are found, remove the group name from the list.
Added arguments to set axis and coord from the command line.
Added a couple of function descriptions, updated get_vols_by_group to take a list of volumes, made the legend size a little smaller, and added a setting for a 1:1 aspect ratio on the plot.