Complements #204.
STLinkV2-1 has F103CB on board! F103C8 on older Stlinks can use upper flash
with hopefully acceptable error rate.
For F103C8 devices, user has to give the force option to dfu-utils.
- Remove connect_assert_srst global.
- Attach functions always release reset.
- Platforms provide a method to poll the reset pin.
- Reset on scan is all internal to command.c
- Reset is released on a failed scan. Fixes#111
