remove Risc.resolve_to_index

mostly by using better typed registers,
which cleans up the code where it was used

lib/risc/instructions/reg_to_byte.rb

@@ -12,9 +12,8 @@ module Risc
   # from and to are translated (from symbol to register if neccessary)
   # but index is left as is.
   def self.reg_to_byte( source , from , to , index)
-    from = resolve_to_register from
-    index = resolve_to_index( to , index)
-    to = resolve_to_register to
+    raise "Not register #{to}" unless RegisterValue.look_like_reg(to)
+    index = to.resolve_index(index) if index.is_a?(Symbol)
     RegToByte.new( source, from , to , index)
   end