Parsing GraphQL IDL shorthand

Same as the Hello world example but shows how to build GraphQL schema from shorthand and wire up some resolvers

Run locally

php -S localhost:8080 ./graphql.php

Try query

curl http://localhost:8080 -d '{"query": "query { echo(message: \"Hello World\") }" }'

Try mutation

curl http://localhost:8080 -d '{"query": "mutation { sum(x: 2, y: 2) }" }'