An Upsert Library

Hello,

So the whole confusion with upserting, upsert directive, and upsert procedure can be a little confusing to a new user. I made a library called quirk that I think can be of use to people who need simple upsert functionality. Maybe this could be a possible addition to the dgo library.

Nice! are you aware of the new upsert transaction?

https://github.com/dgraph-io/dgraph/issues/3059