Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/_csv.pyi

@@ -0,0 +1,51 @@
+import sys
+from typing import Any, Iterable, Iterator, List, Optional, Protocol, Sequence, Text, Type, Union
+
+QUOTE_ALL: int
+QUOTE_MINIMAL: int
+QUOTE_NONE: int
+QUOTE_NONNUMERIC: int
+
+class Error(Exception): ...
+
+class Dialect:
+    delimiter: str
+    quotechar: Optional[str]
+    escapechar: Optional[str]
+    doublequote: bool
+    skipinitialspace: bool
+    lineterminator: str
+    quoting: int
+    strict: int
+    def __init__(self) -> None: ...
+
+_DialectLike = Union[str, Dialect, Type[Dialect]]
+
+class _reader(Iterator[List[str]]):
+    dialect: Dialect
+    line_num: int
+    if sys.version_info >= (3, 0):
+        def __next__(self) -> List[str]: ...
+    else:
+        def next(self) -> List[str]: ...
+
+class _writer:
+    dialect: Dialect
+
+    if sys.version_info >= (3, 5):
+        def writerow(self, row: Iterable[Any]) -> Any: ...
+        def writerows(self, rows: Iterable[Iterable[Any]]) -> None: ...
+    else:
+        def writerow(self, row: Sequence[Any]) -> Any: ...
+        def writerows(self, rows: Iterable[Sequence[Any]]) -> None: ...
+
+class _Writer(Protocol):
+    def write(self, s: str) -> Any: ...
+
+def writer(csvfile: _Writer, dialect: _DialectLike = ..., **fmtparams: Any) -> _writer: ...
+def reader(csvfile: Iterable[Text], dialect: _DialectLike = ..., **fmtparams: Any) -> _reader: ...
+def register_dialect(name: str, dialect: Any = ..., **fmtparams: Any) -> None: ...
+def unregister_dialect(name: str) -> None: ...
+def get_dialect(name: str) -> Dialect: ...
+def list_dialects() -> List[str]: ...
+def field_size_limit(new_limit: int = ...) -> int: ...