Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/wsgiref/headers.pyi

@@ -0,0 +1,31 @@
+import sys
+from typing import List, Optional, Pattern, Tuple, overload
+
+_HeaderList = List[Tuple[str, str]]
+
+tspecials: Pattern[str]  # undocumented
+
+class Headers:
+    if sys.version_info < (3, 5):
+        def __init__(self, headers: _HeaderList) -> None: ...
+    else:
+        def __init__(self, headers: Optional[_HeaderList] = ...) -> None: ...
+    def __len__(self) -> int: ...
+    def __setitem__(self, name: str, val: str) -> None: ...
+    def __delitem__(self, name: str) -> None: ...
+    def __getitem__(self, name: str) -> Optional[str]: ...
+    if sys.version_info < (3,):
+        def has_key(self, name: str) -> bool: ...
+    def __contains__(self, name: str) -> bool: ...
+    def get_all(self, name: str) -> List[str]: ...
+    @overload
+    def get(self, name: str, default: str) -> str: ...
+    @overload
+    def get(self, name: str, default: Optional[str] = ...) -> Optional[str]: ...
+    def keys(self) -> List[str]: ...
+    def values(self) -> List[str]: ...
+    def items(self) -> _HeaderList: ...
+    if sys.version_info >= (3,):
+        def __bytes__(self) -> bytes: ...
+    def setdefault(self, name: str, value: str) -> str: ...
+    def add_header(self, _name: str, _value: Optional[str], **_params: Optional[str]) -> None: ...