Format of BBC Master control block:
Offset	Size	Description	)
 00h	WORD	address of CR-terminated filename
 02h	DWORD	load address of file
 06h	DWORD	execution address of file
 0Ah	DWORD	start address of data to save
 0Eh	DWORD	end address of data to save, or file attributes
		file attributes in low byte (see #03202)
		other three bytes are filing-system specific file attributes