[DOCS] References shared/version and adds doctype to index file (#1280)

* [DOCS] Adds doctype to index file.

* [DOCS] Adds shared/versions to include in index.

Author: szabosteve

docs/index.asciidoc

@@ -1,6 +1,9 @@
 
 = Elasticsearch-PHP
 
+:doctype:           book
+
+include::{docs-root}/shared/versions/stack/{source_branch}.asciidoc[]
 include::{asciidoc-dir}/../../shared/attributes.asciidoc[]
 
 include::overview.asciidoc[]

docs/release-notes.asciidoc

@@ -355,7 +355,7 @@ online document for more information.
   the phpdoc section (for example, 
   https://github.com/elastic/elasticsearch-php/blob/master/src/Elasticsearch/Client.php[$client->rankEval()]). 
   For more information read the 
-  https://www.elastic.co/guide/en/elasticsearch/client/php-api/master/experimental_and_beta_apis.html[experimental and beta APIs] 
+  https://www.elastic.co/guide/en/elasticsearch/client/php-api/{branch}/experimental_and_beta_apis.html[experimental and beta APIs] 
   section in the documentation. 
   https://github.com/elastic/elasticsearch-php/pull/966[#966]
 * Removed `AlreadyExpiredException` since it has been removed