Made directive bindable to models and interpolated text, removed markup generating code.

## Usage:

```javascript
<input type="text" ng-model="input">
<button ui-zeroclip zeroclip-copied="complete($event)" zeroclip-model="input" >Copy</button>

 <button ui-zeroclip zeroclip-copied="copiedText=true" zeroclip-text="This input text: {{ input }}" >Copy</button>
```