non-preemptive kernel reboot

laid out the files:
- npk.asm is the main kernel assembly file
- all the *.inc files are our own assembly libraries, separated for
easier testing
- all the test_*.asm files are for testing the *.inc files with Irvine
stuff like DumpRegs; it won't completely prevent errors from happening
when we switch from DOS to a BIOS-only environment, but it'll help us in
getting rid of general mistakes