Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/@python2/exceptions.pyi

@@ -0,0 +1,50 @@
+from __builtin__ import (
+    ArithmeticError as ArithmeticError,
+    AssertionError as AssertionError,
+    AttributeError as AttributeError,
+    BaseException as BaseException,
+    BufferError as BufferError,
+    BytesWarning as BytesWarning,
+    DeprecationWarning as DeprecationWarning,
+    EnvironmentError as EnvironmentError,
+    EOFError as EOFError,
+    Exception as Exception,
+    FloatingPointError as FloatingPointError,
+    FutureWarning as FutureWarning,
+    GeneratorExit as GeneratorExit,
+    ImportError as ImportError,
+    ImportWarning as ImportWarning,
+    IndentationError as IndentationError,
+    IndexError as IndexError,
+    IOError as IOError,
+    KeyboardInterrupt as KeyboardInterrupt,
+    KeyError as KeyError,
+    LookupError as LookupError,
+    MemoryError as MemoryError,
+    NameError as NameError,
+    NotImplementedError as NotImplementedError,
+    OSError as OSError,
+    OverflowError as OverflowError,
+    PendingDeprecationWarning as PendingDeprecationWarning,
+    ReferenceError as ReferenceError,
+    RuntimeError as RuntimeError,
+    RuntimeWarning as RuntimeWarning,
+    StandardError as StandardError,
+    StopIteration as StopIteration,
+    SyntaxError as SyntaxError,
+    SyntaxWarning as SyntaxWarning,
+    SystemError as SystemError,
+    SystemExit as SystemExit,
+    TabError as TabError,
+    TypeError as TypeError,
+    UnboundLocalError as UnboundLocalError,
+    UnicodeDecodeError as UnicodeDecodeError,
+    UnicodeEncodeError as UnicodeEncodeError,
+    UnicodeError as UnicodeError,
+    UnicodeTranslateError as UnicodeTranslateError,
+    UnicodeWarning as UnicodeWarning,
+    UserWarning as UserWarning,
+    ValueError as ValueError,
+    Warning as Warning,
+    ZeroDivisionError as ZeroDivisionError,
+)