Add initial cable and calculator probing code.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
Tentatively add type IDs for .hpappnote and .hpappprgm, so that beta-testers can play with them, and confirm or infirm.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>
WIP BROKEN Add cables for Prime and 39gII emulators (doesn't exit properly); add broken cable for 39gII HID; refactor and add APIs.

TODO fix virtual cable flushing / closing !

TODO split this commit. For instance, the following changes could be split aside:
* prime_cmd: fixing virtual packet sizes and the addition of write_vtl_pkt;
* prime_vpkt: could also be a separated commit;
* hpcables and fallout in other files: making the "data" argment of cable recv functions a double pointer.

Signed-off-by: Lionel Debroux <lionel_debroux@yahoo.fr>