Extended plugin with new alignTo option / setting

Hi Ray,

We are using a sliding doors technique to create consistent rounded corners (sadly we're still supporting IE7 and 8). Rather than modifying the mark up generated by the plugin to achieve this, we wrapped the select element in mark up similar to this:

`<div class="formField">
    <div class="formElementLeft"></div>
    <div class="formElementInput">
        <select> .... </select>
    </div>
</div>`

This led to the following issue:

![Screen Shot 2013-04-19 at 10 35 51](https://f.cloud.github.com/assets/483733/401263/91f96792-a8d4-11e2-84de-6073d0d1d7f8.png)

As you can see the the formElementLeft pushes out the alignment of the drop down menu. To resolve this we extended the plugin with a new option called alignTo, which allows you to align the drop down menu to a parent element. This resolved our issue:

![Screen Shot 2013-04-19 at 10 39 14](https://f.cloud.github.com/assets/483733/401281/068aa058-a8d5-11e2-8d1f-0370c1331b35.png)

I've added an explanation and usage example in the README.md.

As this is essentially an extension to accommodate browsers that don't support rounded corners I envisage that this feature can be removed in the near future. For now I thought it was worth seeing what your thoughts are. 

All the best