GraphQL Compatibility

Decide whether two GraphQL schemas are compatible, with every finding attributed to the audience it affects. Clients break on a removed field, a removed enum value that is returned, a new required argument, a non-null output turned nullable and a new required input field. Servers break on a new field to resolve, a new interface obligation and an output turned non-null. An enum removal is attributed by where the enum actually flows, computed from the roots.