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/instruction.rb

@@ -0,0 +1,55 @@
+module SlotMachine
+
+  # Base class for SlotMachine instructions
+  # At the base class level instructions are a linked list.
+  #
+  # SlotMachine::Instructions are created by the Sol level as an intermediate step
+  # towards the next level down, the Risc level.
+  # SlotMachine and Risc are both abstract machines (ie have instructions), so both
+  # share the linked list functionality (In Util::List)
+  #
+  # To convert a SlotMachine instruction to it's Risc equivalent to_risc is called
+  #
+  class Instruction
+    include Util::List
+
+    def initialize( source , nekst = nil )
+      @source = source
+      @next = nekst
+      return unless source
+      unless source.is_a?(String) or
+             source.is_a?(Sol::Statement)
+          raise "Source must be string or Instruction, not #{source.class}"
+      end
+    end
+    attr_reader :source
+
+    # to_risc, like the name says, converts the instruction to it's Risc equivalent.
+    # The Risc machine is basically a simple register machine (kind of arm).
+    # In other words SlotMachine is the higher abstraction and so slot instructions convert
+    # to many (1-10) risc instructions
+    #
+    # The argument that is passed is a MethodCompiler, which has the method and some
+    # state about registers used. (also provides helpers to generate risc instructions)
+    def to_risc(compiler)
+      raise self.class.name + "_todo"
+    end
+  end
+
+end
+
+require_relative "label"
+require_relative "check"
+require_relative "simple_call"
+require_relative "dynamic_call"
+require_relative "block_yield"
+require_relative "resolve_method"
+require_relative "truth_check"
+require_relative "not_same_check"
+require_relative "same_check"
+require_relative "jump"
+require_relative "return_jump"
+require_relative "slot_load"
+require_relative "return_sequence"
+require_relative "message_setup"
+require_relative "argument_transfer"