Add EnhancedSerialPort - workaround for Mono's SerialPort.

This PR adds Mono support for SolidSoils4Arduino. The problem with Serial Port on Mono is event OnDataReceived which is not properly implemented. EnhancedSerialPort is a workaround for this problem. Author of EnhancedSerialPort (Antanas Veiverys) has permited (http://antanas.veiverys.com/mono-serialport-datareceived-event-workaround-using-a-derived-class) using this source in SolidSoils4Arduino.