Every time when using Client, you need to include header file "WiFi.h."
connect(ip, port, timeout)/connect(*host, port, timeout): establish a TCP connection.
ip, *host:ip address of target server
port: port number of target server
timeout: connection timeout
connected(): judge whether client is connecting. If return value is 1, then connect successfully; If return
value is 0, then fail to connect.
stop(): stop tcp connection
print(): send data to server connecting to client
available(): return to the number of bytes readable in receive buffer, if no, return to 0 or -1.
read(): read one byte of data in receive buffer
readString(): read string in receive buffer