Added support for Maybe.

Title says it all. 

Works with routes by using the hyphen in the routes : `/#Maybe-Int HandlR GET`.
Handlers use `Maybe` like any other function : `getHandlR :: Maybe Int -> Handler Html`
This implementation is wrong. For example, try parsing "Just X" as Maybe Int. It should end in failure, but instead ends in success parsing Nothing.

You should use <$> instead if $.