v2.0.0-M1

From https://github.com/sangria-graphql-org/sangria/releases/tag/v2.0.0-M1

This is the first milestone release of the 2.x series and the first Sangria release to support Scala 2.13.

Many of Sangria's modules (for marshalling and streaming integrations, etc.) are also now available for 2.13:

• https://github.com/sangria-graphql-org/macro-visit/releases/tag/v0.1.2
• https://github.com/sangria-graphql-org/sangria-argonaut/releases/tag/v1.0.1
• https://github.com/sangria-graphql-org/sangria-circe/releases/tag/v1.3.0
• https://github.com/sangria-graphql-org/sangria-ion/releases/tag/v2.0.0
• https://github.com/sangria-graphql-org/sangria-marshalling-api/releases/tag/v1.0.4
• https://github.com/sangria-graphql-org/sangria-marshalling-testkit/releases/tag/v1.0.2
• https://github.com/sangria-graphql-org/sangria-monix/releases/tag/v2.0.0
• https://github.com/sangria-graphql-org/sangria-spray-json/releases/tag/v1.0.2
• https://github.com/sangria-graphql-org/sangria-streaming-api/releases/tag/v1.0.1

This 2.0.0-M1 release includes several changes:

• Schemas now support descriptions.
• Some deprecated introspection fields have been removed.
• Directives are now allowed on variable definitions.
• There's a new MappedAbstractType transformation.
• There are a number of changes (mostly trivial or to tests) that were needed to support Scala 2.13.

This milestone release is intended primarily to unblock adopters who are migrating to Scala 2.13, and is not guaranteed to be binary compatible with the eventual 2.x series. While these changes are well-tested, this is a pre-release milestone; please use with care and report any issues you come across.