Preparation for Release 3.5.0.

[slaff]

This issue is created to collect all the tasks we need to do before the 3.5.0.

Source Code

• Update Sming/SmingCore/SmingCore.h (Preparation for release 3.5.0. #1295)
• Update Readme.md (Preparation for release 3.5.0. #1295)
• Merge develop into master
• Tag the source code in the master branch

New Features and Improvements

• Updated the Readme and added documentation explaining how to enable LWIP2 or/and SDK 2.1 experimental features (Preparation for release 3.5.0. #1295)
• Better rBoot and spiffs support (Made spiffs_mount() compatible with rBoot. #1292)
• Added method to shutdown a TcpServer ([feature request] Stop a HTTPServer #1272).
• Added Adafruit_BME280 Library (Added Adafruit_BME280 Library #1286).
• Improve websocket ping and pong commands (Initial test code for improved sendPing and sendPong. #1270).
• Added experimental support for SDK 2.1 (Updated Sming to SDK 2.1 #1264).
• Added experimental support for LWIP2 (Added experimental support for LWIP v2 #1289)

All PRs scheduled for this release can be seen from here