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

typings/replay/index.d.ts

@@ -22,6 +22,7 @@ export declare class Replayer {
     play(timeOffset?: number): void;
     pause(): void;
     resume(timeOffset?: number): void;
+    addEvent(event: eventWithTime): void;
     private setupDom;
     private handleResize;
     private getDelay;