code: def distance(self,rng):
      
      if self.chr != rng.chr: return -1
      c = self.cmp(rng)
      if c == 0: return 0
      if c < 0:
        return rng.start - self.end-1
      return self.start - rng.end-1
docs: The distance between two ranges.
  
      :param rng: another range
      :type rng: GenomicRange
      :returns: bases separting, 0 if overlapped or adjacent, -1 if on different chromsomes
      :rtype: int