Fix rendering of nested partials. Tests added.

[stanistan]

Even though it isn't in the spec, both js and php versions of mustache have this behavior.

(use 'clostache.parser)

(let [template "One {{>two}}"  
      d {}
      partials {:two "Two {{>three}}"
                :three "Three {{>four}}"
                :four "Four {{>five}}"
                :five "Five"}]  
  ;; old behavior
  (render template d partials) ;;=> "One Two"

  ;; new behavior
  (render template d partials)) ;;=> "One Two Three Four Five"

[fhd]

Thanks, merged. I'll make a release once I figured out if this should be a feature or fix release :)