@examples syntax

This PR adds the @examples syntax to grunt-qunit-istanbul:

```javascript
/**
 * @examples
 * isInteger(5)     // true
 * isInteger(5.0)   // true
 * isInteger(-5)    // true
 * isInteger(3.14)  // false
 * isInteger('foo') // false
 * isInteger(NaN)   // false
 */
function isInteger(x) {
  return x === Math.floor(x);
}
```

The @examples are run like tests and increase the code coverage. The underlying library is [jsdoc-at-examples](https://github.com/fru/jsdoc-at-examples).