class_docstr: A rule line is a single "Allow:" (allowance==True) or "Disallow:"
  (allowance==False) followed by a path.
code: def __init__(self, path, allowance):
      if path == "" and not allowance:
          # an empty value means allow all
          allowance = True
      path = urllib.parse.urlunparse(urllib.parse.urlparse(path))
      self.path = urllib.parse.quote(path)
      self.allowance = allowance
  
imports: import collections
  import urllib.parse
  import urllib.request
label_desc: Use image node_id 1 to create a new RuleLine object  with example: obj = RuleLine(path, allowance)