Add Python 3 modules, and more Python 2 modules.

Also, sort names alphabetically and add module docstrings.

python3/_warnings.py

@@ -0,0 +1,10 @@
+"""Stub file for the '_warnings' 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 _filters_mutated() -> NoneType: pass
+
+def warn(message, *args, **kwargs) -> NoneType: pass
+
+def warn_explicit(message, category, filename: str, lineno: int, *args, **kwargs) -> NoneType: pass