move mom instruction up one

just like the risc one, also some basic tests

test/mom/test_instruction.rb

@@ -0,0 +1,20 @@
+
+require_relative "helper"
+
+module Mom
+  class TestInstruction < MiniTest::Test
+
+    def test_instantiates
+      assert Instruction.new("Hi")
+    end
+    def test_string_source
+      assert_equal "Hi" ,Instruction.new("Hi").source
+    end
+    def test_nil_next
+      assert_nil Instruction.new("Hi").next
+    end
+    def test_raise
+      assert_raises {Instruction.new(5)}      
+    end
+  end
+end