Delta support - A tale of two firmware versions

Binary deltas of firmware via fwup has been a supported feature for a while. There has also been a kind of rudimentary support for it in NervesHub. We can now remove the word rudimentary. There is now proper delta support in NervesHub. It is not in a tagged release quite yet but NervesCloud runs off of main and so can you if you would benefit from this. (I initially wrote this up for the Nerves…