start to support live mode (#73)

1. add a liveMode flag to config, when liveMode is set, the timer
will keep running even though all the actions casted
2. add a public method addEvent, which will cast newly added event
in sync
3. move mouse in sync mode with the latest position info

src/replay/timer.ts

@@ -45,7 +45,7 @@ export default class Timer {
           break;
         }
       }
-      if (actions.length > 0) {
+      if (actions.length > 0 || self.config.liveMode) {
         self.raf = requestAnimationFrame(check);
       }
     }