Overlap detection and search functionality #9

One feature mentioned by @makeclean is coloring of overlap regions. This shouldn't be too difficult to support (make sure overlap checking is always on in the plotter, add a new negative value to indicate an overlap region, color appropriately).

Another nice feature/tool to add to the plotter would be an overlap "detector" which would slice along a specified interval, stopping when an any overlapping regions are detected and displaying the slice it stopped on.