add overlap option

DESCRIPTION: with the use of centroid as the testing region (see #9 (closed)) a symbol could only have memebership with one region at one level. this is potentially not robust enough. to allow better generalization we could have regions overlap. This is in contrast to a bounding box overlapping multiple regions.

ACCEPTANCE CRITERIA:

• allow a "buffer" option for specs that would buffer regions by a certain percentage of their current size.
• write some unit tests and visualize