Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/@python2/stat.pyi

@@ -0,0 +1,58 @@
+def S_ISDIR(mode: int) -> bool: ...
+def S_ISCHR(mode: int) -> bool: ...
+def S_ISBLK(mode: int) -> bool: ...
+def S_ISREG(mode: int) -> bool: ...
+def S_ISFIFO(mode: int) -> bool: ...
+def S_ISLNK(mode: int) -> bool: ...
+def S_ISSOCK(mode: int) -> bool: ...
+def S_IMODE(mode: int) -> int: ...
+def S_IFMT(mode: int) -> int: ...
+
+ST_MODE: int
+ST_INO: int
+ST_DEV: int
+ST_NLINK: int
+ST_UID: int
+ST_GID: int
+ST_SIZE: int
+ST_ATIME: int
+ST_MTIME: int
+ST_CTIME: int
+S_IFSOCK: int
+S_IFLNK: int
+S_IFREG: int
+S_IFBLK: int
+S_IFDIR: int
+S_IFCHR: int
+S_IFIFO: int
+S_ISUID: int
+S_ISGID: int
+S_ISVTX: int
+S_IRWXU: int
+S_IRUSR: int
+S_IWUSR: int
+S_IXUSR: int
+S_IRWXG: int
+S_IRGRP: int
+S_IWGRP: int
+S_IXGRP: int
+S_IRWXO: int
+S_IROTH: int
+S_IWOTH: int
+S_IXOTH: int
+S_ENFMT: int
+S_IREAD: int
+S_IWRITE: int
+S_IEXEC: int
+UF_NODUMP: int
+UF_IMMUTABLE: int
+UF_APPEND: int
+UF_OPAQUE: int
+UF_NOUNLINK: int
+UF_COMPRESSED: int
+UF_HIDDEN: int
+SF_ARCHIVED: int
+SF_IMMUTABLE: int
+SF_APPEND: int
+SF_NOUNLINK: int
+SF_SNAPSHOT: int