Export directive definitions. (#381)

This exports the ability to define new directives as well as access the built-in @Skip and @include definitions.

Author: leebyron

src/index.js

@@ -51,6 +51,7 @@ export {
   GraphQLInputObjectType,
   GraphQLList,
   GraphQLNonNull,
+  GraphQLDirective,
 
   // Scalars
   GraphQLInt,
@@ -59,6 +60,10 @@ export {
   GraphQLBoolean,
   GraphQLID,
 
+  // Built-in Directives
+  GraphQLIncludeDirective,
+  GraphQLSkipDirective,
+
   // Predicates
   isType,
   isInputType,

src/type/index.js

@@ -35,6 +35,15 @@ export {
   GraphQLNonNull,
 } from './definition';
 
+export {
+  // Directives Definition
+  GraphQLDirective,
+
+  // Built-in Directives
+  GraphQLIncludeDirective,
+  GraphQLSkipDirective,
+} from './directives';
+
 // Common built-in scalar instances.
 export {
   GraphQLInt,