Add `Future` support and example app

[noahemmet]

Hi! I've updated this framework to

• Use SwiftNIO's Futures, instead of GCD.
• Add an example app, which mirrors the default Vapor 3 project structure.
• Fix a couple small GraphiQL bugs.

(Note that until https://github.com/GraphQLSwift/GraphQL/pull/43 is merged, I'm pointing to my custom branch of GraphQLSwift.)

Thanks very much for this framework, I think it will make setting up a Swift GraphQL server much, much easier!

[nonfungibletunji]

Is there a branch o can run now

[noahemmet]

You can add

.package(url: "https://github.com/noahemmet/GraphQLRouteCollection.git", .branch("futures"))

to your Package.swift's dependencies if you'd like to test. Please let me know if you find any bugs or weird behavior!