Fix all Sphinx reference warnings in `Doc/library/urllib.{parse,request}.rst`

Doc/library/urllib.parse.rst:126: py:attr reference target not found: fragment [ref.attr]
Doc/library/urllib.parse.rst:138: py:attr reference target not found: scheme [ref.attr]
Doc/library/urllib.parse.rst:141: py:attr reference target not found: netloc [ref.attr]
Doc/library/urllib.parse.rst:143: py:attr reference target not found: path [ref.attr]
Doc/library/urllib.parse.rst:145: py:attr reference target not found: query [ref.attr]
Doc/library/urllib.parse.rst:147: py:attr reference target not found: fragment [ref.attr]
Doc/library/urllib.parse.rst:149: py:attr reference target not found: username [ref.attr]
Doc/library/urllib.parse.rst:151: py:attr reference target not found: password [ref.attr]
Doc/library/urllib.parse.rst:153: py:attr reference target not found: hostname [ref.attr]
Doc/library/urllib.parse.rst:155: py:attr reference target not found: port [ref.attr]
Doc/library/urllib.parse.rst:160: py:attr reference target not found: port [ref.attr]
Doc/library/urllib.parse.rst:164: py:attr reference target not found: netloc [ref.attr]
Doc/library/urllib.parse.rst:167: py:attr reference target not found: netloc [ref.attr]
Doc/library/urllib.parse.rst:176: py:meth reference target not found: _replace [ref.meth]
Doc/library/urllib.parse.rst:435: py:attr reference target not found: url [ref.attr]
Doc/library/urllib.parse.rst:437: py:attr reference target not found: fragment [ref.attr]
Doc/library/urllib.parse.rst:507: py:meth reference target not found: encode [ref.meth]
Doc/library/urllib.parse.rst:507: py:meth reference target not found: decode [ref.meth]
Doc/library/urllib.parse.rst:575: py:meth reference target not found: encode [ref.meth]
Doc/library/urllib.parse.rst:583: py:meth reference target not found: encode [ref.meth]
Doc/library/urllib.parse.rst:589: py:meth reference target not found: encode [ref.meth]
Doc/library/urllib.parse.rst:599: py:meth reference target not found: decode [ref.meth]
Doc/library/urllib.parse.rst:607: py:meth reference target not found: decode [ref.meth]
Doc/library/urllib.parse.rst:615: py:meth reference target not found: decode [ref.meth]

Doc/library/urllib.request.rst:141: py:attr reference target not found: handler_order [ref.attr]
Doc/library/urllib.request.rst:361: 'envvar' reference target not found: no_proxy [ref.envvar]
Doc/library/urllib.request.rst:667: py:meth reference target not found: http_response [ref.meth]
Doc/library/urllib.request.rst:667: py:meth reference target not found: http_error_404 [ref.meth]
Doc/library/urllib.request.rst:698: py:meth reference target not found: BaseHandler.<protocol>_open [ref.meth]
Doc/library/urllib.request.rst:699: py:meth reference target not found: BaseHandler.http_error_<nnn> [ref.meth]
Doc/library/urllib.request.rst:700: py:meth reference target not found: BaseHandler.<protocol>_request [ref.meth]
Doc/library/urllib.request.rst:701: py:meth reference target not found: BaseHandler.<protocol>_response [ref.meth]
Doc/library/urllib.request.rst:698: py:meth reference target not found: BaseHandler.<protocol>_open [ref.meth]
Doc/library/urllib.request.rst:699: py:meth reference target not found: BaseHandler.http_error_<nnn> [ref.meth]
Doc/library/urllib.request.rst:700: py:meth reference target not found: BaseHandler.<protocol>_request [ref.meth]
Doc/library/urllib.request.rst:701: py:meth reference target not found: BaseHandler.<protocol>_response [ref.meth]