Unify instruction namings also dirs

Was getting confused myself, where it was instruction or instructions, when if the base class was inside or out of dir.
Now dirs are plural, and base class is inside.

lib/slot_machine/instructions/truth_check.rb

@@ -0,0 +1,36 @@
+module SlotMachine
+
+  # The funny thing about the ruby truth is that it is anything but false or nil
+  #
+  # To implement the normal ruby logic, we check for false or nil and jump
+  # to the false branch. true_block follows implicitly
+  #
+  class TruthCheck < Check
+    attr_reader :condition
+
+    def initialize(condition , false_label)
+      super(false_label)
+      @condition  = condition
+      raise "condition must be slot_definition #{condition}" unless condition.is_a?(Slotted)
+    end
+
+    def to_s
+      "TruthCheck #{@condition} -> #{false_label}"
+    end
+
+    def to_risc(compiler)
+      false_label = @false_label.risc_label(compiler)
+      condition_reg = @condition.to_register(compiler,self)
+      
+      compiler.build(self.to_s) do
+        object = load_object Parfait.object_space.false_object
+        object.op :- , condition_reg
+        if_zero false_label
+        object = load_object Parfait.object_space.nil_object
+        object.op :- , condition_reg
+        if_zero false_label
+      end
+    end
+
+  end
+end