add identity function

src/function/identity.js

@@ -0,0 +1 @@
+export default arg => arg;

src/function/index.js

@@ -3,5 +3,6 @@ export { default as combine } from './combine';
 export { default as curry } from './curry';
 export { default as enqueue } from './enqueue';
 export { default as enqueueWithResults } from './enqueueWithResults';
+export { default as identity } from './identity';
 export { default as noop } from './noop';
 export { default as promisify } from './promisify';

src/index.js

@@ -13,6 +13,7 @@ export {
     curry,
     enqueueWithResults,
     enqueue,
+    identity,
     noop,
     promisify
 } from './function';