system.serial.readLine(port [, timeout] [, encoding])
String port - The previously configured serial port to use.
int timeout - Maximum amount of time, in milliseconds, to block before returning. Default is 5000. [optional]
String encoding - The String encoding to use. Default is UTF8. [optional]
String - A line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a line feed.