lib: Add ELF format data structures and procedures
lib: Add multiboot ELF support

This enables retrieving an ELF structure from a multiboot header.
kernel: Obtain elf structure from multiboot header

This adds a global kernel elf structure which is initialised at boot
time.
arch/x86: Print symbol names in backtrace

This transforms:

#0  [0x1018C7]
#1  [0x101636]
#2  [0x100231]

into:

#0  [0x1018C7] panic
#1  [0x101636] k_main
#2  [0x100231] start
kernel/panic: Add an empty line before backtrace
tools: Rename headercheck.sh -> listincludes.sh
tools/listincludes: Add support for command line args

Instead of automatically generating a list of all header files, this
allows a list of .h files to be passed as arguments.