Merge tag 'v4.0.0' into develop

Bump version to 4.0.0

Author: valeros

platform.json

@@ -17,7 +17,7 @@
     "type": "git",
     "url": "https://github.com/platformio/platform-espressif8266.git"
   },
-  "version": "4.0.0-rc.1",
+  "version": "4.0.0",
   "frameworks": {
     "arduino": {
       "package": "framework-arduinoespressif8266",