t.i._pollingfile : module documentation

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