Graphql-core

This release is a halfway-point between 0.4.12 and 0.4.13, containing the validation stuff that's been implemented so far.

- Added support for experimental schema validation 37.

This release updates feature parity to `graphql-js` v0.4.11.

Changelog
- Fix typo in directive schema introspection description.
- 32 Implement `concat_ast` utility
- 33 Allow providing directives to `GraphQLSchema`
- 34 Allow nested objects with similar keys.
- 35 Support deprecation via introspection
- 36 Fix false positive validation error from fragment cycle when unknown fragment is used.

We're happy to announce `graphql-core` v0.4.9 is a stable release and is ready for use in Production.

Changelog
- Implement `subscription` type execition in the schema. 27
- Clearer lex errors for unprintable unicode.
- Introspection descriptions for scalar and introspection query types.
- Add missing tests. 23
- Implement [RFC] Additional optional arguments. 26
- Bump required gevent to `1.1rc1`.

Getting ready for stable release.

Changelog:
- [Executor] Implement memoization on `get_argument_values`.
- [Type Definition] Implement `__hash__` methods on `GraphQLField` and `GraphQLArgument`.
- [AST Visitor] Check if edit in visitor is a valid node.
- GraphQLUnion shall now accept a callable for types. This will make functionality equivalent to all the other types. i.e. GraphQLInterfaceType and GraphQLObjectType when it comes to defining fields/interfaces/types.

This is the first beta release of `graphql-core` and represents feature parity with [`graphql-js`](https://github.com/graphql/graphql-js/) `v0.4.7`, hence the matching version number. All `graphql-core` releases will follow `graphql-js` in terms of version numbers. This means for a given version of graphql-js, you can expect feature parity on the same version of `graphql-core`.

We will follow GraphQL's semantic versioning and releases except for one key difference, we will be introducing a BUGFIX version number as well, in the form of `MAJOR.MINOR.PATCH.BUGFIX`. This will allow us to match the PATCHes in graphql-js, while maintaining our own bugfix version numbers. That means that `v0.4.7.0`, `v0.4.7.1` will all match `v0.4.7` in feature parity, but with bugfixes to the Python codebase.