time: implement pub fn since(t Time) Duration

vlib/time/time.v

@@ -121,10 +121,9 @@ pub fn (t Time) add_days(days int) Time {
 	return t.add(days * 24 * time.hour)
 }
 
-// since returns a number of seconds elapsed since a given time.
-fn since(t Time) int {
-	// TODO Use time.Duration instead of seconds
-	return 0
+// since returns the time duration elapsed since a given time.
+pub fn since(t Time) Duration {
+	return now() - t
 }
 
 // relative returns a string representation of the difference between t

vlib/time/time_test.v

@@ -244,3 +244,13 @@ fn test_offset() {
 
 	assert diff_seconds == time.offset()
 }
+
+fn test_since() {
+	t1 := time.now()
+	time.sleep(20 * time.millisecond)
+	d1 := time.since(t1)
+	assert d1 >= 20_000_000
+	time.sleep(20 * time.millisecond)
+	d2 := time.since(t1)
+	assert d2 >= 40_000_000
+}