Minimal implementation for reading/writing files in the root
directory of a FAT16/FAT32 file system.
Can read/write from raw disk devices, and no longer relies on
operating system support for mounting the file system.
Currently assumes Imager will always be run on 'little endian'
architectures such as Intel and ARM (at least under Linux).
If there is a use-case for big-endian (anybody still using Sparc?)
this may be revisited later.
