fix Delay component

Hello, and first of all thanks for Crafty :)

I've had two issues with the Delay component:

- The .delay() method returns the length of the _delays array (return value of push()), instead of the entity itself. That means that developers can't chain more methods after the .delay(). Try this in the console:

```javascript
Crafty.e("2D, Color, Delay")
      .color("#ff0000")
      .attr({ x: 10, y: 10, w: 10, h: 10 }
      .delay(function(){this.attr({ x: 20, y: 20 });}, 1000)

// returns 1

Crafty.e("2D, Color, Delay")
      .color("#ff0000")
      .delay(function(){this.attr({ x: 20, y: 20 });}, 1000)
      .attr({ x: 10, y: 10, w: 10, h: 10 })

// returns TypeError: Object 1 has no method 'attr'
```

- The component keeps all of its triggered delays in the _delays array and doesn't delete them. That takes up too much memory when you have repeated delays (see below). BTW, feature request - maybe make them easier to create? Or am I missing something here?

```javascript
var repeatedFunc = function () {
  // do something and then:
  this.delay(function(){repeatedFunc.call(this);},1000);
};
// start the madness
this.delay(function(){repeatedFunc.call(this);},1000);
```

I'm trying to fix this in my two commits.

The return one is easy, just do the push and then return this.

The other one works by setting a purge flag when we mark a delay as triggered, then after the whole loop has run, creating a new array with untriggered delays if the flag is set.

---

Just as a side question: is there some kind of these delays defined in terms of frames, not milliseconds, built in Crafty at the moment? I had to create my own FrameDelay component ... :) If you'd like, I can document it and share it in next Pull Request.