Add support for twitter bootstrap css style , with nested def

Hello,

I wanted to use your gem for displaying Twitter Bootstrap for RTL (hebrew), and saw that there is no support for the nested @media declaration, so I tried to add the support , and managed to do it by changing the r2 function and the reg-ex.

I tested it in my app with bootstrap rtl, and it works great, I did not manage to execute tests (I am still learning ) 
Hope you will use it in your gem.
please let me know if you find any issues .

Thanks,

Haim Lankry

If we have the string : " h1 {padding:3px;} @media (size=40){h1 {margin:20px;padding:3px;}} "
The new Regexp is : /([^\{\}]+[^\}]|[\}])+?/
we will get the results:

Match 1
h1 {
Match 2
padding:3px;
Match 3
}
Match 4
@media (size=40){
Match 5
h1 {
Match 6
margin:20px;padding:3px;
Match 7
}
Match 8
}