Get the latest poll with shortcode [poll id='latest']

Hey.
I've made a small change to allow to show the latest home page.
One of my clients wanted this. Whenever she added a new poll, she had to update what poll is to be shown on her home page. This was a pain. 
So, created this. Please merge it into the next version if you are OK with it.

Thank You.
-Varun Srinivas
Co-Founder SudoSaints
www.sudosaints.com