Added Alignment Feature

Updated the plugin to support 'left', 'center' and 'right' alignment of items in relation to the parent container.

By default the 'center' option is set. Users can change this behaviour by passing in an 'align' argument to the plugin options with a value of 'left', 'center', 'right'.

Example:
```js
var options = {
    align: 'left',
    autoResize: true,
    offset: 10,
    container: $('.example'),
    itemWidth: 226
};

$('.example li').wookmark( options );
```