This release brings up graphql-go on par with graphql-js v0.4.18

Notable changes:

• Move the extension definition out of type definition
• [RFC] Type condition optional on inline fragments.
  • Implements https://github.com/facebook/graphql/pull/100
• [RFC] Make operation name optional.
  • Implements https://github.com/facebook/graphql/pull/99
• Spec compliant Int sizing
  • graphql.Int now enforces strict compliance to the spec.
  • int and uint that exceeds 2^32 will be considered as invalid graphql.Int
  • Added/updated scalars_serialization_test.go to reflect the changes
• Experimental: customisable validation
  • Changed function signature for graphql.NewTypeInfo() to accept a struct.
  • Allows the possibility to remove the experimental FieldDefFn params

Changes to public/exported vars / func