- Make RelativeSize public so we can use it in non-member functions
- Make a template out of matching the string suffixes; this is
safer because the length of the suffix can be computed at compile-time
(+1 for the trailing NUL) rather than writing it out in boilerplate.
- Non-functional as yet, WIP
- Intended for use on SBC images and similar, which need to resize
the root partition to the size of the SD card they're on.
FIXES#921
