Support currency/dollar value

[cogentParadigm]

Thanks for sharing this work! I would like to parse dollar values in my expression, for example:

$1,500.75 - $200.00

I'm not sure the best way to do this, but it looks like I can create a custom Lexer and add a token definition with an custom pattern that will match dollar values.

However, I would still need to parse the token into a float. For TokenType::RealNumber this happens in the Node::factory method which is called from the private function shuntingYard in the the Parser class. This doesn't look easily extendable.

Do you have any suggestions on how I should go about this?