FDC - double-sided disk (first step of 2 steps) :
- readID does increment, MultiTrack is taken into account
- SCAN() command added
- DELETE() command added and faked (same as WRITE/READ)
- physical HD/logical H/info TS implemented
- ST1/ST2 protections taken into account
- is_seeking state added

TODO :
- TRACK NOT FOUND
- SECTOR NOT FOUND
- seeking-end undo while changing disk
- End of Cylinder (index flag)

TEST :
- Tested with PROTEXT and ROMDOS XL 4.0 : second disk drive can insert DOS D2 dsk (80tds)
- A simple .bas file is saved as 4KB in t40ss DATA disk (without ROMDOS it is 1KB here), and in DOS D2 dsk.
- A simple .bas file seem bad saved as 2KB in t80ds IBM disk, so one .bas on two does run fine (but nice pointed), but cat display some 750KB size, strange.
- Since is_seeking state was added, FutureOS does detect disk but does not list correctly content yet.
- Macadam ERE protected dsk does still lock, it has a missing TRACK in fact (TRACK NOT FOUND, I think)