Make Maybe.none singleton

[Lonli-Lokli]

I think it will be useful to have none from maybe singleton, to allow direct comparison two values - and because obviously different nones should be equal.
It might be a breaking change, of course .

[JSMonk]

Done

[Lonli-Lokli]

I mean make it non function but constant as well

[JSMonk]

I think having a function for one value and a field for another is not a good idea. The API in this case will be slightly inconsistent. But, I'm open to discussing it, why do you think it would be better to have the none field?