Redesign fs_dev, raw_dev, introducing device_partition and switch_fs. ...

In theory, one could mount an encrypted FAT partition itself coming from a disk image, etc.

Rewrote crt0, init, and chainloading code ...

start.s, init.c, linker.ld and linker.specs are meant
to be re-used by user applications, should they remove the defines
from init.c and the .chainloader* sections from the linker script

fusee: update header names for starting cpu0

Change fusee folder naming