Fragment cache implementation

when you `render @quotes`, the generated key may look like this, just pasted development log:

"Read fragment views/quotes/9-20130720122218255167000/quotes/8-20130720115809199272000/quotes/7-20130720115813013080000/quotes/1-20130720115852294819000/8ecde2451f7dc8e9ee72c716192ee072 (0.3ms)"

```ruby
"quotes/#{quote_id}-#{quote_updated_at}" + another quote + another quote... 
  #{template tree digest}"
```

![screen shot 2013-07-20 at 9 37 55 pm](https://f.cloud.github.com/assets/184520/830193/41496240-f139-11e2-9434-51b120da53d1.png)

http://api.rubyonrails.org/classes/ActionView/Helpers/CacheHelper.html#method-i-cache