Add example of using proxy to wrap a non-final java object and override one of its methods.

[jumarko]

This uses ZipFile just as an example:

(let [filename "empty.zip"
      original-zip (ZipFile. filename)
      proxy-zip (proxy [ZipFile] [filename]
                  ;; overriding close method
                  (close [] (println "Ignored!"))
                  ;; random method implementation passing the call to the wrapper
                  (size [] (.size original-zip)))]
  [[(.size proxy-zip) (.size original-zip)]
   ;; check the REPL - you will see "Ignored!" printed one time
   ;; - note that we cannot return "Ignored" as a value
   ;; because close method is 'void'
   [(.close proxy-zip) (.close original-zip)]])