* syntax: repeatable directive definitions (by @bojanserafimov)
* syntax: support for nameless queries with vars (by @timsuchanek)
* syntax: support interfaces that implement other interfaces (by @obi1kenobi)
* api: `into_static` method for values (by @mathstuf)
* security: guard against stack overflow for deeply nested input (by @That3Percent)
* api: `consume_definition` function (by @That3Percent)