Adding a new LESS CSS plugin

The reference code repo

https://github.com/zerg000000/cryogen-less.git

It required one lines of changes in the core project( the `dorun` line).

``` clojure
(sass/compile-sass->css!
{:src-sass sass-src
:dest-sass (str "../public" blog-prefix "/" sass-dest)
:ignored-files ignored-files
:base-dir "resources/templates/"})
(dorun (map #(apply (resolve (symbol %)) [config]) (:extra config)))))
```