Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/email/header.pyi

@@ -0,0 +1,26 @@
+from email.charset import Charset
+from typing import Any, List, Optional, Tuple, Union
+
+class Header:
+    def __init__(
+        self,
+        s: Union[bytes, str, None] = ...,
+        charset: Union[Charset, str, None] = ...,
+        maxlinelen: Optional[int] = ...,
+        header_name: Optional[str] = ...,
+        continuation_ws: str = ...,
+        errors: str = ...,
+    ) -> None: ...
+    def append(self, s: Union[bytes, str], charset: Union[Charset, str, None] = ..., errors: str = ...) -> None: ...
+    def encode(self, splitchars: str = ..., maxlinelen: Optional[int] = ..., linesep: str = ...) -> str: ...
+    def __str__(self) -> str: ...
+    def __eq__(self, other: Any) -> bool: ...
+    def __ne__(self, other: Any) -> bool: ...
+
+def decode_header(header: Union[Header, str]) -> List[Tuple[bytes, Optional[str]]]: ...
+def make_header(
+    decoded_seq: List[Tuple[bytes, Optional[str]]],
+    maxlinelen: Optional[int] = ...,
+    header_name: Optional[str] = ...,
+    continuation_ws: str = ...,
+) -> Header: ...