Add Tags combinator

[nakaji-dayo]

I propose Tags combinator.
Like the Summary and Description combinator, this is useful for servant-swagger.
Swagger tags: https://swagger.io/docs/specification/2-0/grouping-operations-with-tags/

Can this be added to the main repo?
I can send PR.

[alpmestan]

@phadej Thoughts?

[phadej]

Well, indeed we have Summary and Description. But Tags IMHO start to be too swagger-y (and arbitrary).

I don't really know.

[domenkozar]

It's currently possible to do this via http://hackage.haskell.org/package/servant-swagger-1.1.5/docs/Servant-Swagger.html#g:3

[alpmestan]

@nakaji-dayo See the previous comment. That should cover your needs, right?

[domenkozar]

we can close this as duplicate of haskell-servant/servant-swagger#73