Panic now disables interrupts and prints a message

It's a little weird because kprintf also calls panic if it has a
problem, but panic uses kprintf...
Added the NULL pointer definiton to inttypes
Added stack_size and 4KIB allocation code

The physical allocator should be complete now. The code needs to be
cleaned up and commented, but for the most part everything should work
fine. The allocator should also do all allocation and free operations in
constants time, which is nice.
Moved memset into kernel/klib.c
Added the beginnings of the kernel C library

Added memset
Initial paging/virtual memory functions

This is the start of the implementation of different virtual memory
functions. Things become much easier now that there is a dedicated
virtual mapping of the entire physical address space.