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

lib/risc/instructions/operator_instruction.rb

@@ -13,7 +13,7 @@ module Risc
   class OperatorInstruction < Instruction
     def initialize( source , operator , left , right )
       super(source)
-      operator = operator.value if operator.is_a?(Vool::Constant)
+      operator = operator.value if operator.is_a?(Sol::Constant)
       @operator = operator
       raise "unsuported operator :#{operator}:#{operator.class}:" unless Risc.operators.include?(operator)
       @left = left

lib/risc/parfait_boot.rb

@@ -141,7 +141,7 @@ module Parfait
       Type: {names: :List , types: :List  ,
              object_class: :Class, methods: :CallableMethod ,
              is_single: :Object} ,
-      VoolMethod: { name: :Word , args_type: :Type , frame_type: :Type } ,
+      SolMethod: { name: :Word , args_type: :Type , frame_type: :Type } ,
       Word: {char_length: :Integer , next_word: :Word} ,
       }
   end