Please add export for isNew in new release.

[AcidBurnHen]

Due to my custom needs in building a backend for my application I have extended the package.json to export isNew from symbol. So that I can use a validation check if the session is new and easily import it with import { isNew } from "next-session/lib/symbol"; . I am writing here as a suggestion to add this to the official release if possible as I think that isNew, isTouched and isDestroyed can give us more freedom to write some custom functionalities.