Optional epsilon: number = EPSILONan optional epsilon
an array of clusters, where each cluster is a list of indices which point to the "ranges" input array.
Given a list of unsorted ranges, each range being a pair of numbers, this method will create clusters where every range in the cluster is overlapped by at least one other range. Range pairs do not necessarily need to be in increasing order.
a list of ranges, each range a pair of numbers