rename register to risc

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

test/risc/test_collector.rb

@@ -0,0 +1,11 @@
+require_relative "../helper"
+
+module Risc
+  class TestCollector < MiniTest::Test
+    def test_simple_collect
+      Machine.new.boot
+      objects = Risc::Collector.collect_space
+      assert ((350 < objects.length) or (430 > objects.length)) , objects.length.to_s
+    end
+  end
+end