add type hint for system

stubs/pydu/system.pyi

@@ -0,0 +1,19 @@
+import os
+from typing import Callable, List
+from pydu.platform import WINDOWS
+
+
+def makedirs(path: str, mode: int=0o755, ignore_errors: bool=False, exist_ok: bool=False) -> None: ...
+def remove(path: str, ignore_errors: bool=False, onerror: Callable=None) -> None: ...
+def removes(paths: List[str], ignore_errors: bool=False, onerror: Callable=None) -> None: ...
+def open_file(path: str, mode: str='wb+', buffer_size: int=-1, ignore_errors: bool=False) -> None: ...
+def copy(src: str, dst: str, ignore_errors: bool=False, follow_symlinks: bool=True) -> None: ...
+def touch(path: str) -> None: ...
+def chmod(path: str, mode: int, recursive: bool=False) -> None: ...
+def which(cmd: str, mode: int=os.F_OK | os.X_OK, path: str=None) -> None: ...
+if WINDOWS:
+    class chcp(object):
+        def __init__(self, code: str) -> None: ...
+else:
+    def symlink(src: str, dst: str, overwrite: bool=False, ignore_errors: bool=False) -> None: ...
+    def link(src: str, dst: str, overwrite: bool=False, ignore_errors: bool=False) -> None: ...