Doxyfile.in

The currently used image is 404 so use an inline image instead.

Change-Id: I56a0d187fd06dc2c5c370e6532d89815ccec63d6
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1451
Tested-by: jenkins