Fix ruby normalising to_vool

So that vool layer never has complex conditions or returns
Start with while, next if, return and assign

lib/vool/statements.rb

@@ -33,6 +33,9 @@ module Vool
     def shift
       @statements.shift
     end
+    def pop
+      @statements.pop
+    end
 
     # to_mom all the statements. Append subsequent ones to the first, and return the
     # first.