basic immutability for type

add_instance_variable now uses global type list to check
adds hash and to_has functions
use backdoor (send) for booting

lib/soml/compiler/class_field.rb

@@ -10,7 +10,7 @@ module Soml
       index = for_class.instance_type.variable_index(statement.name)
       #raise "class field already defined:#{name} for class #{for_class.name}" if index
       #puts "Define field #{name} on class #{for_class.name}"
-      index = for_class.instance_type.add_instance_variable( statement.name , statement.type )
+      for_class.instance_type.add_instance_variable( statement.name , statement.type )
 
       return nil # statements don't reurn values, only expressions
     end