Fixed case where there are duplicate value arguments

For instance, using all value type options parameters, the libary would not parse "Pull 10/1/13 10/1/13", the tokenizer would condense this into two tokens, "Pull 10/1/13".

The root causes is that .Except returns the set difference, rather than the bag difference, which removes duplicates. I reimplemented using lists and filter clauses, rather than excepts.