Sometimes we want to roll-back to a previous firmware version.
To do so we need a higher riotbot version numbers still.
Add an update command to the riotboot_gen_hdr tool so that an existing
firmware image can be re-rolled out with a new version number.
In order to use the RIOT bootloader (riotboot) a header needs to
be created and placed before the firmware. This tool generates
such a header with the expected information by the bootloader.
Co-authored-by: Kaspar Schleiser <kaspar@schleiser.de>
