Semantic versioning for the firmware

[cheery]

I'm sure there will be other places where you might want to change the API or details on how the firmware works. It's inevitable that this will happen.

Give semantic version numbering for the firmware, and remember to update it. As in addition you could provide a file, which tells how backwards compatibility was broken and why.

[popcornmix]

"vcgencmd version" will indicate a version number for firmware.
Each vchiq service reports a version number which is incremented on an API change.
E.g. look at peer_version in alsa driver
https://github.com/raspberrypi/linux/blob/rpi-3.6.y/sound/arm/bcm2835-vchiq.c