Re-organize directory structure (#4971)

See discussion in #2491

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

stubs/croniter/METADATA.toml

@@ -0,0 +1,2 @@
+version = "0.1"
+python2 = true

stubs/croniter/croniter.pyi

@@ -0,0 +1,43 @@
+import datetime
+from typing import Any, Dict, Iterator, List, Optional, Text, Tuple, Type, TypeVar, Union
+
+_RetType = Union[Type[float], Type[datetime.datetime]]
+_SelfT = TypeVar("_SelfT", bound=croniter)
+
+class CroniterError(ValueError): ...
+class CroniterBadCronError(CroniterError): ...
+class CroniterBadDateError(CroniterError): ...
+class CroniterNotAlphaError(CroniterError): ...
+
+class croniter(Iterator[Any]):
+    MONTHS_IN_YEAR: int
+    RANGES: Tuple[Tuple[int, int], ...]
+    DAYS: Tuple[int, ...]
+    ALPHACONV: Tuple[Dict[str, Any], ...]
+    LOWMAP: Tuple[Dict[int, Any], ...]
+    bad_length: str
+    tzinfo: Optional[datetime.tzinfo]
+    cur: float
+    expanded: List[List[str]]
+    start_time: float
+    dst_start_time: float
+    nth_weekday_of_month: Dict[str, Any]
+    def __init__(
+        self, expr_format: Text, start_time: Optional[Union[float, datetime.datetime]] = ..., ret_type: Optional[_RetType] = ...
+    ) -> None: ...
+    # Most return value depend on ret_type, which can be passed in both as a method argument and as
+    # a constructor argument.
+    def get_next(self, ret_type: Optional[_RetType] = ...) -> Any: ...
+    def get_prev(self, ret_type: Optional[_RetType] = ...) -> Any: ...
+    def get_current(self, ret_type: Optional[_RetType] = ...) -> Any: ...
+    def __iter__(self: _SelfT) -> _SelfT: ...
+    def __next__(self, ret_type: Optional[_RetType] = ...) -> Any: ...
+    def next(self, ret_type: Optional[_RetType] = ...) -> Any: ...
+    def all_next(self, ret_type: Optional[_RetType] = ...) -> Iterator[Any]: ...
+    def all_prev(self, ret_type: Optional[_RetType] = ...) -> Iterator[Any]: ...
+    def iter(self, ret_type: Optional[_RetType] = ...) -> Iterator[Any]: ...
+    def is_leap(self, year: int) -> bool: ...
+    @classmethod
+    def expand(cls, expr_format: Text) -> Tuple[List[List[str]], Dict[str, Any]]: ...
+    @classmethod
+    def is_valid(cls, expression: Text) -> bool: ...