changes:

1. add UV_LOOP_TIMEOUT_OBSERVER for uv_loop_option.
   observer function call when backend timeout of uv loop changed.
   for interrupt your self event loop.

2. uv_backend_fd return iocp handle in windows.
   for call GetQueuedCompletionStatus your self.

3. add uv_insert_overlapped_result windows specific function.
   for pass result of GetQueuedCompletionStatus to uv loop.

Example case for win32 gui application:
in main thread just run default win32 message loop.

while(GetMessage(&msg,NULL,0,0)){
  TranslateMessage(&msg);
  DispatchMessage(&msg);
}

create a window to handle uv events in it's WndProc.

if(msg == WM_UV_READY){
  if(lparam)uv_insert_overlapped_result(loop, (LPOVERLAPPED)lparam); 
  uv_run(loop, UV_RUN_NOWAIT);
}

create a thread to poll iocp events.

LPOVERLAPPED overlapped;
while(1){
  GetQueuedCompletionStatus(... overlapped, timeout_);
  SendMessage(hwnd, WM_UV_READY, 0, overlapped);  
}

in timeout observer function, interrupt GetQueuedCompletionStatus

void on_timeout_change(... timeout){
  timeout_ = timeout;
  PostQueuedCompletionStatus(iocp,0,0,NULL);
}
uv_loop_configure(loop, UV_LOOP_TIMEOUT_OBSERVER, on_timeout_change);