Epspd command set.

The commands accepted by the epspd utility are a subset of the commands
implemented by the Epson TF-20 floppy drive unit. This is logic as the 
PX-4/PX-8 does not use the utility/drive to boot, as the HX-20 does.

The epspd command set:

epspd name     FNC code   epson name
DS_SEL         0x0E       Select Disk
FDC_RESET      0x0D/0x0E  System Reset  (both PX-4 and PX-8)
FDC_READ       0x77       * \
FDC_WRITE      0x78       *  | not in the incomplete doc I have
FDC_WRITEHST   0x79       * /
FDC_COPY       0x7A       Disk all copy
FDC_FORMAT     0x7C       Disk formatting (FRMAT)


