PrinterPort

The PrinterPort interface is used to physically access the printer. There are 2 classes implementing 
the PrinterPort interface:
	FilePort: writes into operating system file which represent the parallel port. For example 
			"PRN:" in windows or "/dev/lpr" for Linux. If can also write to a network 
			printer using the syntax "//computername/printername". 

			Example of use: FilePort port=new FilePort("PRN:");

	HDParallelPort: access the printer using the commapi package (see installation). This can 
			only access local printers and requires the installation od the commapi 
			however it read printer responses like "error", "out of paper" or printer 
			"on-line". 
	
			Example of use: HDParallelPort port=new HDParallelPort("LPT1");

The PrinterPort class is passed to the TextPrinter.startJob() method.