add set_internal

and the set_slot with register
very much like the get_slot for get_internal

lib/register/instructions/set_slot.rb

@@ -22,7 +22,8 @@ module Register
       @register = register
       @array = array
       @index = index
-      raise "not integer #{index}" unless index.is_a? Numeric
+      raise "index 0 " if index == 0
+      raise "Not integer or reg #{index}" unless index.is_a?(Numeric) or RegisterValue.look_like_reg(index)
       raise "Not register #{register}" unless RegisterValue.look_like_reg(register)
       raise "Not register #{array}" unless RegisterValue.look_like_reg(array)
     end