reimplement instruction listeners with indexes

easier to understand, as indexes map to Binarycode indexes, and can thus later be used to assemble directoy into the  code
Almost no change in tests (now only multiples of 4 addresses allowed)

lib/parfait/binary_code.rb

@@ -47,6 +47,12 @@ module Parfait
       @next
     end
 
+    def last_code
+      last = self
+      last = last.next while(last.next)
+      last
+    end
+
     def each_block( &block )
       block.call( self )
       @next.each_block( &block ) if @next