Support GraphQL

@janl:
> http://graphql.org
>
> It’s rather new, but getting good traction. This would be a nice addition to our API. Somebody might already be hacking on this ;)
>
> critique: http://kellysutton.com/2017/01/02/do-we-need-graphql.html

@davisp:
> That article also mentions JSON API that could be interesting to read up on. I skimmed the front page a bit and it seems similarly interesting to GraphQL.

@gr2m:
>I created a JSON API spec for common account tasks:
>view: http://docs.accountjsonapi.apiary.io/
>source: https://github.com/hoodiehq/account-json-api
>
>JSON API is coming from the Ember community and it has some downsides. But it’s create to just avoid all bikeshedding around REST API design and just follow a common specification. There are other similar projects. And weather it’s a first class citizen feature or some kind of plugin, I think it would be nice for CouchDB to "own" the CouchDB/JSON API story. Meaning, if someone googles "CouchDB JSON API", they should come to one of our landing pages where we describe who the two work together.
>
>The same could be for GraphQL. I think someone build a system that has a GraphQL API but also uses PouchDB somehow to make it work offline ... ? I tried to find it but no luck. ping @nolanlawson do you know of something?

@nolanlawson:
> Yes there is this: https://github.com/MikeBild/graphql-pouch

Start by reviewing the GraphQL reference, the linked JSON API discussion, and the graphql-pouch project mentioned in the thread. The issue names no files, tests, or implementation boundary, so first clarify whether GraphQL support belongs in CouchDB itself or an accompanying project, and define the supported API surface before implementation.

Written by the indexing model from the issue text.