Rename Vool to Sol

Simple is really the descriptive name for the layer
Sure, it is "virtual" but that is not as important as the fact that it is simple (or simplified)
Also objct (based really) is better, since orientated implies it is a little like that, but only orientated, not really it. Sol only has objects, nothing else
Just cause i was renaming anyway

test/sol/test_return.rb

@@ -0,0 +1,56 @@
+require_relative "helper"
+
+module Sol
+  class TestReturnSlotMachine < MiniTest::Test
+    include SolCompile
+
+    def setup
+      @compiler = compile_main( "return 5")
+      @ins = @compiler.slot_instructions.next
+    end
+
+    def test_class_compiles
+      assert_equal SlotLoad , @ins.class , @ins
+    end
+    def test_slot_is_set
+      assert @ins.left
+    end
+    def test_two_instructions_are_returned
+      assert_equal 5 ,  @ins.length
+    end
+    def test_slot_starts_at_message
+      assert_equal :message , @ins.left.known_object
+    end
+    def test_slot_gets_return
+      assert_equal :return_value , @ins.left.slots[0]
+    end
+    def test_slot_assigns_something
+      assert @ins.right
+    end
+    def test_slot_assigns_int
+      assert_equal SlotMachine::IntegerConstant ,  @ins.right.known_object.class
+    end
+    def test_second_is_return
+      assert_equal ReturnJump,  @ins.next(1).class
+    end
+    def test_array
+      check_array [SlotLoad, ReturnJump, Label, ReturnSequence, Label], @ins
+    end
+  end
+  class TestReturnSendSlotMachine < MiniTest::Test
+    include SolCompile
+
+    def setup
+      @compiler = compile_main( "return 5.div4" , "Integer.div4" )
+      @ins = @compiler.slot_instructions.next
+    end
+
+    def test_return_is_last
+      assert_equal ReturnJump , @ins.next(4).class
+    end
+    def test_array
+      check_array [MessageSetup, ArgumentTransfer, SimpleCall, SlotLoad, ReturnJump ,
+                    Label, ReturnSequence, Label] , @ins
+    end
+  end
+end