Made example code easier to read by duplicating Auth factory (#823)

Author: reyesh

docs/guide/user-auth.md

@@ -307,7 +307,7 @@ app.config(["$routeProvider", function($routeProvider) {
     templateUrl: "views/home.html",
     resolve: {
       // controller will not be loaded until $waitForSignIn resolves
-      // Auth refers to our $firebaseAuth wrapper in the example above
+      // Auth refers to our $firebaseAuth wrapper in the factory below
       "currentAuth": ["Auth", function(Auth) {
         // $waitForSignIn returns a promise so the resolve waits for it to complete
         return Auth.$waitForSignIn();
@@ -319,7 +319,7 @@ app.config(["$routeProvider", function($routeProvider) {
     templateUrl: "views/account.html",
     resolve: {
       // controller will not be loaded until $requireSignIn resolves
-      // Auth refers to our $firebaseAuth wrapper in the example above
+      // Auth refers to our $firebaseAuth wrapper in the factory below
       "currentAuth": ["Auth", function(Auth) {
         // $requireSignIn returns a promise so the resolve waits for it to complete
         // If the promise is rejected, it will throw a $stateChangeError (see above)
@@ -338,6 +338,12 @@ app.controller("AccountCtrl", ["currentAuth", function(currentAuth) {
   // currentAuth (provided by resolve) will contain the
   // authenticated user or null if not signed in
 }]);
+
+app.factory("Auth", ["$firebaseAuth",
+  function($firebaseAuth) {
+    return $firebaseAuth();
+  }
+]);
 ```
 
 ### `ui-router` Example
@@ -362,7 +368,7 @@ app.config(["$stateProvider", function ($stateProvider) {
       templateUrl: "views/home.html",
       resolve: {
         // controller will not be loaded until $waitForSignIn resolves
-        // Auth refers to our $firebaseAuth wrapper in the example above
+        // Auth refers to our $firebaseAuth wrapper in the factory below
         "currentAuth": ["Auth", function(Auth) {
           // $waitForSignIn returns a promise so the resolve waits for it to complete
           return Auth.$waitForSignIn();
@@ -375,7 +381,7 @@ app.config(["$stateProvider", function ($stateProvider) {
       templateUrl: "views/account.html",
       resolve: {
         // controller will not be loaded until $requireSignIn resolves
-        // Auth refers to our $firebaseAuth wrapper in the example above
+        // Auth refers to our $firebaseAuth wrapper in the factory below
         "currentAuth": ["Auth", function(Auth) {
           // $requireSignIn returns a promise so the resolve waits for it to complete
           // If the promise is rejected, it will throw a $stateChangeError (see above)
@@ -394,6 +400,12 @@ app.controller("AccountCtrl", ["currentAuth", function(currentAuth) {
   // currentAuth (provided by resolve) will contain the
   // authenticated user or null if not signed in
 }]);
+
+app.factory("Auth", ["$firebaseAuth",
+  function($firebaseAuth) {
+    return $firebaseAuth();
+  }
+]);
 ```
 Keep in mind that, even when using `ng-annotate` or `grunt-ngmin` to minify code, that these tools
 cannot peer inside of functions. So even though we don't need the array notation to declare our