Use consistent indentation within this file.

No functional change.
XXX: this file is missing a license.
Split MI definitions from machine/os.h into os.h
continue header cleanup

remove empty mini-os/traps.h and include mini-os/machine/traps.h
minor header + whitespace cleanup
Implement _exit (we _must_ not return from a __noreturn__ function)
set progname (the easiest way, to be revisited)
avoid console output silently dropping characters