Fixed problem, I forgot to refer to the global variables adding the earmuffs!

To call the program, I just have to write:
   clisp -i guess-my-number.lisp
Fixed some more problems.

   * misspelling on the definition of *lower-limit*
   * ash function required one extra parameter, that I missed to add
Added a couple of new functions, bigger and smaller, to play the game.
Added some instructions about how this works
Fixed my first problem trying to match the parenthesis.

As the song for lisp said, in the end I will eat parentheses for breakfast, and
more paretheses for lunch.
Added implementation for start-over.

I will read chapters, 2.5 and 2.6, and then I'll do some freestyle changes on
this simple game.