add distribution specific stuff

[AshyPinguin]

This PR allows distributions to customise the final raspinfo script with their specific not found help messages. It could easily be expended to more.

It is still wip because I want to make it usable for other tools too, but feel free to review or edit stuff!

[pelwell]

You're going to have to sell this change a lot more than you are. It's a shame that you taking what used to be standalone script that could be installed with curl and forcing people to use CMake.

[chewi]

While I appreciate you trying to improve things for Gentoo, I think this may be overdoing it. The raspinfo script isn't essential, so it doesn't need to have perfect output on Gentoo. It would just be nice if it didn't blow up in your face.

[AshyPinguin]

You're going to have to sell this change a lot more than you are. It's a shame that you taking what used to be standalone script that could be installed with curl and forcing people to use CMake.

I didn't get that intent sorry.

[AshyPinguin]

You're going to have to sell this change a lot more than you are. It's a shame that you taking what used to be standalone script that could be installed with curl and forcing people to use CMake.

I don't think I've to sell it anymore, because I added a check that checks if it has been parsed by cmake and prints defaults if it hasn't.

Sorry for not doing anything with it for four weeks. I had some other stuff to worry about.