Update documentation

Author: sothawo

src/main/asciidoc/reference/elasticsearch-new.adoc

@@ -1,6 +1,16 @@
 [[new-features]]
 = What's new
 
+[[new-features.4-3-0]]
+== New in Spring Data Elasticsearch 4.3
+
+* Upgrade to Elasticsearch 7.15.0.
+* Allow runtime_fields to be defined in the index mapping.
+* Add native support for range field types by using a range object.
+* Add repository search for nullable or empty properties.
+* Enable custom converters for single fields.
+* Supply a custom `Sort.Order` providing Elasticsearch specific parameters.
+
 [[new-features.4-2-0]]
 == New in Spring Data Elasticsearch 4.2