Add basic paging stuff
Needs much tidying up
Merge irq.c and isr_handler.c into interrupt.c
Also check if handlers are registered in isr_handler
Proper PANIC macro and function
Fix term_print_hex
Previously numbers containing 4 binary 0s anywhere other than at the
start of the number would be printed wrong
Add ASSERT macro
Don't assume ints are 32 bits in term_printf
May as well avoid that assumption where possible, in order to increase
portability
Add dynamic memory allocation