Added time left function.

FossilOrigin-Name: 9fa6601d10b08c28a7e6768ffeec0d5a5fc0413854e454a919503c5a775dd0d8

src/cw/timer.h

@@ -55,6 +55,13 @@ typedef time_t cw_timer_t;
  */
 #define cw_timer_timeout(t) (time(NULL)>(t) ? 1 : 0)
 
+/**
+ * Get the number of seconds left in a timer
+ * @param t timer
+ * @return number of seconds
+ */
+#define cw_timer_timeleft(t) ((t)-time(NULL))
+
 /**
  * Get the number of nano seconds from a timeval.
  */