Add to Stackage

[AshleyYakeley]

I notice categories is not in Stackage. Should it be added?

[ekmett]

I tend not to add things directly to stackage that I plan to heavily change the API of in the future.

That said, folks add stuff I write to stackage by transitively depending on them all the time.

I'll eventually be replacing much of the API of categories, though, so take that into consideration.