- usb/usb.h (USB_LANGID_ENGLISH_US): added USB LANGID for US-English
- board.h (board_sernum), board.c (board_sernum, hex, get_sernum,
board_init): provide the board's serial number in "board_sernum"
(UTF-encoded)
- sernum.h (sernum_get_descr), sernum.c (sernum_get_descr): return
string descriptors for the serial number
- descr.c (device_descriptor), usb/dfu.c (device_descriptor):
set iSerialNumber if serial number is available
- atusb.c (main), usb/dfu.c (my_descr): call sernum_get_descr for
unknown descriptors
- Makefile (OBJS, BOOT_OBJS): added sernum.o
