#5910: Run daemon as a service on Windows

Factor out demonization implementation to platform-specific files.
Implement daemonization on Windows using service API. Improve *NIX
implementation by handling signals asynchronously to prevent potential
issues of running complex code inside the handler.

daemon/daemon.h

@@ -0,0 +1,29 @@
+/*
+ * This file Copyright (C) 2015 Mnemosyne LLC
+ *
+ * It may be used under the GNU GPL versions 2 or 3
+ * or any future license endorsed by Mnemosyne LLC.
+ *
+ * $Id$
+ */
+
+#ifndef DTR_DAEMON_H
+#define DTR_DAEMON_H
+
+struct tr_error;
+
+typedef struct dtr_callbacks
+{
+  int  (*on_start)       (void * arg, bool foreground);
+  void (*on_stop)        (void * arg);
+  void (*on_reconfigure) (void * arg);
+}
+dtr_callbacks;
+
+bool dtr_daemon (const dtr_callbacks  * cb,
+                 void                 * cb_arg,
+                 bool                   foreground,
+                 int                  * exit_code,
+                 struct tr_error     ** error);
+
+#endif /* DTR_DAEMON_H */