Add Python 3 modules, and more Python 2 modules.

Also, sort names alphabetically and add module docstrings.

python3/atexit.py

@@ -0,0 +1,16 @@
+"""Stub file for the 'atexit' module."""
+# This is an autogenerated file. It serves as a starting point
+# for a more percise manual annotation of this module.
+# Feel free to edit the source below, but remove this header when you do.
+
+def _clear() -> NoneType: pass
+
+def _ncallbacks() -> long: pass
+
+def _run_exitfuncs() -> NoneType: pass
+
+def register(*args, **kwargs) -> object:
+    raise TypeError()
+    raise MemoryError()
+
+def unregister(*args, **kwargs) -> NoneType: pass