Add a package for modelling cards

Time to do the fun non-yakshaving part.  I'll start out by writing
some custom types for the objects of concern: ranks, suits, cards and
sets of cards.

cantedraw.asd

@@ -2,6 +2,7 @@
   :components ((:file "packages")
                (:file "lib.macros")
                (:file "lib.functions")
+               (:file "model")
                (:file "main"))
   :build-operation "program-op"
   :build-pathname "bin/cantedraw"