Support microdata in fivestar

Ok, so this patch should kind of work.

To test it:

1. Enable microdata module
2. Create a Product content type
3. In microdata settings for the content type, enter itemtype: http://schema.org/Product, title itemprop: name
4. Add a rating field. Be sure to use the Stars (rated while editing) widget, the patch doesn't yet work with the other widgets
5. On the field config form, under "Default Microdata Mappings", select schema.org and click Use Default Mapping. This should fill in the fields with the defaults.
6. Save the content type
7. Create a new piece of content and rate it
8. Paste the following in the body field (Rich Snippets need a certain amount of related data before they display)
   

     <div itemprop="offers" itemscope itemtype="http://schema.org/Offer">
       <span itemprop="price">$55.00</span>
       <link itemprop="availability" href="http://schema.org/InStock" />In stock
     </div>
   
     Product description:
     <span itemprop="description">0.7 cubic feet countertop microwave.
     Has six preset cooking categories and convenience features like
     Add-A-Minute and Child Lock.</span>
   
     Customer reviews:
   
     <div itemprop="reviews" itemscope itemtype="http://schema.org/Review">
       <span itemprop="name">Not a happy camper</span> -
       <span itemprop="description">The lamp burned out and now I have to replace
       it. </span>
     </div>
   
     <div itemprop="reviews" itemscope itemtype="http://schema.org/Review">
       <span itemprop="name">Value purchase</span> -
       <span itemprop="description">Great microwave for the price. It is small and
       fits in my apartment.</span>
     </div>
   

9. Test the output at http://www.google.com/webmasters/tools/richsnippets ... it should show stars

Great, thanks for testing! If you have any suggestions for how something could work better, let me know.

Eric, if you want to give a look at the code and see if the way it works makes sense, that would be really helpful... I'm trying to make sure there aren't any DX WTFs.