rename register to risc

seems to fit the layer much better as we really have a very reduced
instruction set

test/vm/method_compiler/test_field_access.rb

@@ -1,12 +1,12 @@
 require_relative "helper"
 
-module Register
+module Risc
   class TestFields < MiniTest::Test
     include ExpressionHelper
     include AST::Sexp
 
     def setup
-      Register.machine.boot
+      Risc.machine.boot
     end
 
     def test_field_not_defined
@@ -26,7 +26,7 @@ module Register
       add_space_field(:bro,:Object)
       @root = :field_access
       @input = s(:field_access,s(:receiver, s(:known, :self)),s(:field,s(:ivar, :bro)))
-      @output = Register::RegisterValue
+      @output = Risc::RiscValue
       check
     end