Implements a simple polling interface for file descriptors that don't work with select() - this is pretty much only useful on Windows.
| Class | _PollableResource | Undocumented |
| Class | _PollingTimer | Undocumented |
| Class | _PollableReadPipe | Undocumented |
| Class | _PollableWritePipe | No class docstring; 4/10 methods documented |