Support for WP Rest API paging (#1733)

* Update README.md

Unecessary per_page mention in readme

* Simplify `httpExceptionHandler` with es6

* Add function that gets multiple WP pages

* Allow perPage to be configurable (with default of 10)

* Add auth to paginated requests

* Rename pagination function

* Fix exception handler

* Lint gatsby-node.js

* Add babel dependencies/config

* Don’t pass perPage parameter around

* Remove unused variable

* Code cleanup

* Default `per_page` to 100

* Use WP total pages header & code style and style format

* Revert "Add babel dependencies/config"

This reverts commit 973d85b.

packages/gatsby-source-wordpress/README.md

@@ -95,23 +95,6 @@ The Authentication on Wordpress.com is not supported yet. This means that you wo
   ]
 ```
 
-
-### How to raise the default and maximum number of posts to be returned in result set from REST API
-
-To modify the `per_page` `default` and `maximum` arguments add the following to your functions.php
-
-```php
-  add_filter( 'rest_endpoints', function( $endpoints ){
-      if ( ! isset( $endpoints['/wp/v2/posts'] ) ) {
-          return $endpoints;
-      }
-      $endpoints['/wp/v2/posts'][0]['args']['per_page']['default'] = 200; // defaults to 10
-      $endpoints['/wp/v2/posts'][0]['args']['per_page']['maximum'] = 200; // defaults to 100
-      return $endpoints;
-  });
-```
-
-
 ## How to query : GraphQL
 
 You can query nodes created from Wordpress using GraphQL like the following: