HEADER (NEW) command implemented

The HEADER command is succesfully implemented. Quick refresher on this BASIC 4.0 command:

header "name",d*[,onu*][,i**]

If the i** optional parameter is provided, the entire disk is formatted, otherwise only the BAM/directory are formatted (faster). In either case, all files are deleted. A full format (i.e. WITH identifier) of a Seagate 850 MB drive took 65 minutes. A quick-format (i.e. without identifier) of the same drive took just 5 minutes.