Modified the definition of 'Dao.NewParser.GenTokenizer' so that they can return multiple tokens.  This is necessary to allow tokenizers to make smarter decisions while analyzing text, for example if if the "data" keyword is found the next tokenizer should tokenize arbitrary base-64 encoded text rather than simply returning right away and let the next tokenizer try to analyze the base-64 text.  Tokenizing with this behavior requires the the tokenizer to see the "data" keyword then tokenize the base-64 text and return both tokens. Tokenizers can now do this with the modifications made today. I have also added several generally useful tokenizers.