Add stubs for CGIHTTPServer (#3196)

This commit adds:
* Stubs for CGIHTTPServer in the Python 2 standard library, as requested in #1147.
* Stubs for six.moves.CGIHTTPServer in Python 2, as requested in #22.

stdlib/2/CGIHTTPServer.pyi

@@ -0,0 +1,8 @@
+# Stubs for CGIHTTPServer (Python 2.7)
+
+from typing import List
+import SimpleHTTPServer
+
+class CGIHTTPRequestHandler(SimpleHTTPServer.SimpleHTTPRequestHandler):
+    cgi_directories: List[str]
+    def do_POST(self) -> None: ...

third_party/2/six/moves/CGIHTTPServer.pyi

@@ -0,0 +1 @@
+from CGIHTTPServer import *

third_party/2/six/moves/__init__.pyi

@@ -36,7 +36,7 @@ from . import http_client
 from . import email_mime_text
 # import email.MIMEBase as email_mime_base
 from . import BaseHTTPServer
-# import CGIHTTPServer as CGIHTTPServer
+from . import CGIHTTPServer
 from . import SimpleHTTPServer
 from . import cPickle
 from . import queue