move interpreter to register

seems more where it belongs, since it interprets the register machine
instructions

test/compiler/fragments/helper.rb

@@ -1,5 +1,5 @@
 require_relative '../../helper'
-require "interpreter/interpreter"
+require "register/interpreter"
 
 # Fragments are small programs that we run through the interpreter and really only check
 # - the no. of instructions processed
@@ -16,7 +16,7 @@ module Fragments
     machine = Register.machine.boot
     machine.parse_and_compile @string_input
     machine.collect
-    @interpreter = Interpreter::Interpreter.new
+    @interpreter = Register::Interpreter.new
     @interpreter.start machine.init
     count = 0
     begin