Add Retweet/Favorite Counts Format String

Format string of retweet/favorite count number is unavailable in current format string items, but I think it should be very usable if adding them. ˊ・ω・ˋ
![twmode-favcount](https://cloud.githubusercontent.com/assets/1370070/5009494/7310b25e-6aa2-11e4-8ce1-0b3fd4919a2a.png)

And add some color... 
![twmode-favcount1](https://cloud.githubusercontent.com/assets/1370070/5016934/223bdca8-6ae5-11e4-826f-bdf2917b5bb9.png)

```lisp
(setq twittering-status-format
      "%i %s,%FACE[font-lock-preprocessor-face]{%p} %FACE[font-lock-comment-face]{%@}:
%FOLD[  ]{%T %FACE[font-lock-comment-face]{// from %f%L%r%R} %FACE[font-lock-keyword-face]{%e} %FACE[font-lock-function-name-face]{%F}}
 ")
```