🔨 Features

• Additional API MqttClient::setCleanSession (#12)
• Extending debug output to display size of transmitted MQTT message (#28)
• Fixing some warnings and wrap ESP8266 Client overrides in #ifdef (#22)
• Fixing error caused due to compiler being unable to resolve overloaded functions (#30)
• Add all WiFi enabled boards as CI build targets (#32)
• Adding an additional ArduinoMqttClient constructor as well as a method setClient to allow late initialisation (#37)
• Remove obsolete workaround for ESP8266 in compilation test CI workflow (#38)