Sass中的字符串替换

简单的临时解决方案（以Mac为例）：

$ git clone -b string_functions https://github.com/chriseppstein/sass
$ cd sass
$ sudo rake install

$ sudo mv /usr/bin/sass /usr/bin/sass.orig
$ sudo ln -s /Library/Ruby/Gems/1.8/gems/sass-3.2.0.alpha.0/bin/sass /usr/bin/sass