[src] Intel assembly syntax in boot.S. Makefile supports debug mode.

The initial AT&T assembly syntax in boot.S has been adopted to Intel
assembly sytax.

The projects' Makefile has been extended in such a way
that it may boot a kernel into a 'debug' mode. This way, it is possible
to debug the kernel running inside qemu-kvm. Follow isntructions stated
directly within the Makefile for debugging.