Draft implementation of CTRL-C fix for Win32.

Fixes issue #100.

This is a preliminary pull request to generate discussion.  Proper integration in documentation to be refined, testing on Linux/etc. TBD.
pywin32 isn't importable on platforms other than Windows, as are many windows-specific utilities like this. I guess I'm not sure why this would be a special case.

You can always have a dummy context manager with:

```python
@contextmanager
def dummy(action):
    yield
```

If you really feel strongly, you can either protect the ctypes calls in the win32.py module with conditions, or split it into two files (win32.py and _win32.py) with your existing logic just moved to `win32.py` from `__init__.py`. The ctypes code should definitely not be triggered when importing anything else in utils.