add support for binaries behind boot loaders on device

[kilograham]

If the boot loader itself contains binary info which points to the other binaries, we could support this

[earlephilhower]

Sounds like a good plan! As long as the binary_info_header_redirect (or whatever) is defined in such a way that it can be static even as its target (real) app changes, should be easy to support in OTA/2ndary bootloaders. I suppose that's kind of a given since the binary_info_header of the real app is always placed immediately after its vector table, and normally the real app starting flash address is always constant too.