Refactor fusee's makefile

Revamp all the Makefiles (thanks @fincs @WinterMute) ...

... dependencies are now properly handled (e.g. header changes, 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

Change fusee folder naming