Refactors layout of Release notes page.

docs/releasenotes.asciidoc

@@ -7,18 +7,13 @@ reference fields by leafnode. For example, the `geoip.country_code` field can no
 from previous versions of Kibana.
 
 [float]
-[[key-features]]
-== Key Features
+[[enhancementss]]
+== Enhancements
 
 * {k4issue}2855[Issue 2855]: You can now configure Kibana log levels.
 * {k4issue}4204[Issue 4204]: Kibana now has a plugin manager.
 * {k4pull}4951[Pull Request 4951]: New UI to support plugin context changes.
 * {k4issue}3270[Issue 3270]: Kibana now displays a server status page.
-
-[float]
-[[improvements]]
-== Improvements
-
 * {k4issue}2245[Issue 2245]: You can now customize the descriptions shown in the visualization.
 * {k4pull}4702[Pull Request 4702]: Dark theme added to dashboards.
 * {k4issue}1902[Issue 1902]: Tile maps support configurable WMS-compliant map servers.