implement smaller than comparison

which is NOT an operator in the risc sense
rather a minus and a check for sign
(which _could be more efficient in arm, with conditional execution)

lib/risc/boot.rb

@@ -184,7 +184,7 @@ module Risc
       Risc.operators.each do |op|
         obj.instance_type.add_method Builtin::Integer.operator_method(op)
       end
-      [:putint, :div4, :div10].each do |f|   #div4 is just a forward declaration
+      [:putint, :div4, :div10 , :<].each do |f|   #div4 is just a forward declaration
         obj.instance_type.add_method Builtin::Integer.send(f , nil)
       end
     end