libcoro

fix some Codacy problems, remove mutable from signal_win32

handle close on zero bytes in the client, generic function for WinSock read/write

timer_handle: remove mutables, use RegisterWaitForSingleObject instead of thread-alert callbacks

io_notifier_iocp: using GetQueuedCompletionStatusEx instead of GetQueuedCompletionStatus for batched events

Remove unused file