docs: def string_to_genomic_range(rstring):
    """ Convert a string to a genomic range
  
    :param rstring: string representing a genomic range chr1:801-900
    :type rstring:
    :returns: object representing the string
    :rtype: GenomicRange
    """
    m = re.match('([^:]+):(\d+)-(\d+)',rstring)
    if not m: 
      sys.stderr.write("ERROR: problem with range string "+rstring+"\n")
    return GenomicRange(m.group(1),int(m.group(2)),int(m.group(3)))