Split stdlib into Python 2 and 3 versions (#5442)

All new files in stdlib/@python2 are straight copies of the
corresponding files in stdlib.

stdlib/@python2/readline.pyi

@@ -0,0 +1,40 @@
+import sys
+from _typeshed import AnyPath
+from typing import Callable, Optional, Sequence
+
+_CompleterT = Optional[Callable[[str, int], Optional[str]]]
+_CompDispT = Optional[Callable[[str, Sequence[str], int], None]]
+
+def parse_and_bind(__string: str) -> None: ...
+def read_init_file(__filename: Optional[AnyPath] = ...) -> None: ...
+def get_line_buffer() -> str: ...
+def insert_text(__string: str) -> None: ...
+def redisplay() -> None: ...
+def read_history_file(__filename: Optional[AnyPath] = ...) -> None: ...
+def write_history_file(__filename: Optional[AnyPath] = ...) -> None: ...
+
+if sys.version_info >= (3, 5):
+    def append_history_file(__nelements: int, __filename: Optional[AnyPath] = ...) -> None: ...
+
+def get_history_length() -> int: ...
+def set_history_length(__length: int) -> None: ...
+def clear_history() -> None: ...
+def get_current_history_length() -> int: ...
+def get_history_item(__index: int) -> str: ...
+def remove_history_item(__pos: int) -> None: ...
+def replace_history_item(__pos: int, __line: str) -> None: ...
+def add_history(__string: str) -> None: ...
+
+if sys.version_info >= (3, 6):
+    def set_auto_history(__enabled: bool) -> None: ...
+
+def set_startup_hook(__function: Optional[Callable[[], None]] = ...) -> None: ...
+def set_pre_input_hook(__function: Optional[Callable[[], None]] = ...) -> None: ...
+def set_completer(__function: _CompleterT = ...) -> None: ...
+def get_completer() -> _CompleterT: ...
+def get_completion_type() -> int: ...
+def get_begidx() -> int: ...
+def get_endidx() -> int: ...
+def set_completer_delims(__string: str) -> None: ...
+def get_completer_delims() -> str: ...
+def set_completion_display_matches_hook(__function: _CompDispT = ...) -> None: ...