Share buttons in entry footer

I added share buttons to my personal blog a while ago, figured you might want to include it in the official Leggero theme. I think it would make sense to have such buttons, as we're in the social media era, big time. 

![share1](https://f.cloud.github.com/assets/6784705/2306070/c548160e-a278-11e3-8a06-54f55e621dfd.PNG)

Thanks!