Support the monitor interface on Windows as well

This change required sacrificing both code cleanliness and the specific
error reports from perror(). Those could have been kept with a portable
wrapper, but that's too much work. We'll do it if unforseen errors
arise.

src/Monitor.hpp

@@ -1,7 +1,5 @@
 #pragma once
 
-#ifndef _WIN32
-
 #include "CNProtocol.hpp"
 
 #include <list>
@@ -12,5 +10,3 @@ namespace Monitor {
     void tick(CNServer *, time_t);
     void start(void *);
 };
-
-#endif // _WIN32