Autolinker can exceed the call stack

The code below will result in `Uncaught RangeError: Maxiumum call stack exceeded`:

``` js
var test = function() {
    var t = [];
    for (var i = 0; i < 50000; i++) {
        t.push(' /&gt;&lt;br');
    };
    return t.join('');
};
a = new Autolinker();
var result = a.link(test());
```
