Refactor ready:script to support new notify framework

Follow-up to abcb3ce, calling the service ready:script when readiness
has been signaled to or detected by Finit.

Issue #300

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/service.h

@@ -41,6 +41,7 @@ int       service_timeout_after  (svc_t *svc, int timeout, void (*cb)(svc_t *svc
 int       service_timeout_cancel (svc_t *svc);
 
 void      service_forked         (svc_t *svc);
+void      service_ready          (svc_t *svc);
 
 int       service_stop           (svc_t *svc);
 int       service_step           (svc_t *svc);