Add the empty function never : Never -> a

[andersk]

This adds the missing destructor for the empty Never type. See elm-lang/core#593 for discussion.

[mgold]

Would this be caught and rejected once elm-lang/core#873 elm/compiler#873 is fixed?

[andersk]

@mgold Depends on the details. Of the possible definitions
never1 (Never n) = never1 n
never2 n = never2 n
never3 = never3
we would certainly want to accept never1 and reject the buggy never3, but one could imagine reasonable implementations that either accept or reject never2.

[jvoigtlaender]

I would be very surprised if the Elm compiler would at some point reject the never2 definition.

[jvoigtlaender]

Now published: http://package.elm-lang.org/packages/elm-community/basics-extra/1.0.0/.