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.