add api for button
add api for button

itead/ITEADLIB_Arduino_Nextion,itead/ITEADLIB_Arduino_Nextion,itead/ITEADLIB_Arduino_Nextion,FireDeveloper/ITEADLIB_Arduino_Nextion,itead/ITEADLIB_Arduino_Nextion,FireDeveloper/ITEADLIB_Arduino_Nextion