Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/@python2/robotparser.pyi

@@ -0,0 +1,7 @@
+class RobotFileParser:
+    def set_url(self, url: str): ...
+    def read(self): ...
+    def parse(self, lines: str): ...
+    def can_fetch(self, user_agent: str, url: str): ...
+    def mtime(self): ...
+    def modified(self): ...