implement cert issue

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)

add usign-exec.c

create C function wrappers calling the /usr/bin/usign executable and
processing the results.

usign_v()   : usign -V ...
usign_s()   : usign -S ...
usign_f_*() : usign -F ...

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)

start implementing loading cert from filesystem, add validity times

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)

add external blob and internal blobmsg data structures

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)

add shim executable and CMakeLists

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)

add COPYING license file

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)

add .gitignore

Signed-off-by: Daniel Golle <[email protected]>
This work was sponsored by WIO (wiowireless.com)