v0.13.0

This release brings several breaking changes. Please refer to the UPGRADE document for details.

New features and notable changes:

• PHP version required: 7.1+
• Spec compliance: error category and extensions are displayed under extensions key when using default formatting (#389)
• New experimental executor with improved performance (#314).
  It is a one-line switch: GraphQL::useExperimentalExecutor(). Please try it and post your feedback in #397 (as it may become the default one in future)
• Ported extendSchema from the reference implementation under GraphQL\Utils\SchemaExtender (#362)
• Added ability to override standard types via GraphQL::overrideStandardTypes(array $types) (#401)
• Added flag Debug::RETHROW_UNSAFE_EXCEPTIONS which would only rethrow app-specific exceptions (#337)
• Several classes were renamed (see UPGRADE.md)
• Schema Validation improvements