new: TimeMetric: split

assira/src/main/java/net/ranides/assira/time/TimeMetric.java

@@ -53,7 +53,13 @@ public final class TimeMetric {
     public long time() {
         return time(unit);
     }
-    
+
+    public long split() {
+        long dt = stop();
+        start();
+        return dt;
+    }
+
     public long time(TimeUnit unit) {
         return time(unit, stack.peek());
     }