- XBee API with multi-serial support

This code is based off of the original XBee API library for Arudino.  However, that code only supported the main serial UART /Serial/, and I needed it to support the four serial lines on the Arduino Mega 2560.  Thus, this fork was created.

Normally you would initialize the XBee function as such:

	void setup() {
		xbee.begin(9600);
	}

but now, you can set what serial port you want to bind the XBee to, like this

	void setup() {
		xbee.setSerial(Serial3);
		xbee.begin(9600);
	}

Easy peasy!