event now checks if link is blacklisted before actually preloading 

Additionally I've added the functionality to preload images.
For this to work I had to rework the init() function, so it now takes an object as only parameter

InstantClick can now be initiated like this:
```javascript
InstantClick.init(
    {[delay: <int> [, mousedown: true|false [, preload: true|false [, whitelist: true|false ]]]]}
);
```
thus `InstantClick.init(true);` is replaced by `InstantClick.init({whitelist: true});`, 

`InstantClick.init(50, true);` is now `InstantClick.init({delay: 50, whitelist: true});`, 

and `InstantClick.init('mousedown', true)` is `InstantClick.init({mousedown: true, whitelist: true});`