Added describe-location function.

While reading I was wondering why it is needed to call cadr and not only cdr to
get the description. So I tried in the REPL to reproduce the story:

   First assoc retrieves a list, which contains and index and another element
   (another list in this case).
      [1]> (assoc 'living-room *nodes*)
      (LIVING-ROOM (YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH.))

   By calling cadr, we get exactly what we want, the second element, without
   the initial list it contains it.
      [2]> (cadr (assoc 'living-room *nodes*))
      (YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH.)

   Just a cdr, gets also the element, but embedded in another list.
      [3]> (cdr (assoc 'living-room *nodes*))
      ((YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH.))
Added new data and a function to determine the options the player can take.

The function describe-path, is a bit weird, but after observing how it should
work,  I found that is quite tied to the data it can read from,
So (describe-path '(garden next door)), after applying the function, will
return something like: (there is a door going west from here).
Fix. A backstick is not the same as an apostrophe.

I'd say that the first one, allows the evaluation of certain parts of the list.
According to the book this is what's called quasiquoting ("quasiquoting: allows
to create chunks of data that have small pieces of Lisp code embedded in them)
Added a new function to apply to *edges* so that we get what we need

It would have been more natural for me to start from here, instead of making
first describe-paths and then this one. But is good for the purposes of the
book.
Funny way of writing a "map".

1]> (describe-paths 'living-room *edges*)
(THERE IS A DOOR GOING WEST FROM HERE. THERE IS A LADDER GOING UPSTAIRS FROM HERE.)
Objects, association between objects and locations, as well as a function to determine which objects are in a certain location added.

Weird stuff added. New functionality to detect which objects are in a certain
location added.
Fix: objects-at was not working due to the unnamed function was using an undefined arg.
Added new function to describe-objects at a given location.

More understandable after a while looking a lisp. But still a bit ugly ... why
mapcar and not just "map", why labels instead of anonymous or lambda functions,
why #', not so nice.
Anyways here is the result

[1]> (describe-objects 'living-room *objects* *object-locations*)
(YOU SEE A WHISKEY ON THE FLOOR. YOU SEE A BUCKET ON THE FLOOR.)
Added a "look" function to allow the user get a description of where he/she is.

This new function ties all together for the game. It's capable of describing
any location where the user is (determined by *location*). The game is ready to
roll

[1]> (look)
(YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH. THERE IS
A DOOR GOING WEST FROM HERE. THERE IS A LADDER GOING UPSTAIRS FROM HERE. YOU
SEE A WHISKEY ON THE FLOOR. YOU SEE A BUCKET ON THE FLOOR.)
Added "walk" function.

All the pieces are fitting together.

[1]> (look)
(YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH. THERE IS A DOOR GOING WEST FROM HERE. THERE IS A LADDER GOING UPSTAIRS FROM HERE. YOU SEE A WHISKEY ON THE
 FLOOR. YOU SEE A BUCKET ON THE FLOOR.)
[2]> (walk 'west)
(YOU ARE IN A BEATIFUL GARDEN. THERE IS A WELL IN FRONT OF YOU THERE IS A DOOR GOING EAST FROM HERE. YOU SEE A CHAIN ON THE FLOOR.)
[3]> (walk 'east)
(YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH. THERE IS A DOOR GOING WEST FROM HERE. THERE IS A LADDER GOING UPSTAIRS FROM HERE. YOU SEE A WHISKEY ON THE
 FLOOR. YOU SEE A BUCKET ON THE FLOOR.)
[4]> (walk 'upstairs)
(YOU ARE IN THE ATTIC. THERE IS A GIGANT WELDING TORCH IN THE CORNER. THERE IS A LADDER GOING DOWNSTAIRS FROM HERE.)
[5]> (walk 'downstairs)
(YOU ARE IN THE LIVING-ROOM. A WIZZARD IS SNORING LOUDLY ON THE COUCH. THERE IS A DOOR GOING WEST FROM HERE. THERE IS A LADDER GOING UPSTAIRS FROM HERE. YOU SEE A WHISKEY ON THE
 FLOOR. YOU SEE A BUCKET ON THE FLOOR.)
[6]>

However, writing this last function was not that easy to understand, due to the
amount of parenthesis. I guess that in the end I will eat parenthesis for
breakfast, and eat more parenthesis for lunch!