Added guessing game example.

This is from some sample code I put up on Rosetta Code a few months back:
  * http://rosettacode.org/wiki/Guess_the_number#LFE
  * http://rosettacode.org/wiki/Guess_the_number/With_Feedback#LFE
Merge branch 'add-guessing-game-example' of https://github.com/oubiwann/lfe into develop