code: def coverageCounts(self):
          
          coverageCounts = Counter()
          for start, end in self._intervals:
              coverageCounts.update(range(max(0, start),
                                          min(self._targetLength, end)))
          return coverageCounts
docs: For each location in the subject, return a count of how many times that
          location is covered by a read.
  
          @return: a C{Counter} where the keys are the C{int} locations on the
              subject and the value is the number of times the location is
              covered by a read.