Fix operation of `sign.command` when printable characters occur
immediately before `=BEGIN OC VAULT=`. `strings` finds the location of
the first printable character in such a sequence. `hexdump` automatically
works on 16 byte boundaries, so still finds the correct offset.
Use `BASE_ALIGNAS` to enforce the required alignment, which will not be
correct on all builds unless enforced (note alignment is required purely
for locating the structure correctly from external script as above, not
for reading in C).
Remove struct packing, since structs had better be naturally packed anyway
(if not, reading from them without arbitrary-alignment-safe code, as we
do, would be undefined behaviour). Add static asserts to confirm expected
size as required by `sign.command`.
Update the docs to refer to `sign.command` rather than to include the
signing commands explicitly - otherwise we have two places that need to
be kept in sync for signing commands, and note that the commands in the
two places were already out of sync.
Signed-off-by: Mike Beaton <mjsbeaton@gmail.com>
