Add more documentation to the redox kernel

See merge request redox-os/kernel!95

Use older linked_list_allocator version

See merge request redox-os/kernel!92

Fix compilation error for graphical_debug

See merge request redox-os/kernel!91

Fix TODO: Use triple fault to guarantee reboot

Cause interrupt, since the IDT is dorked we can't find the INT 3
handler (double fault), and the double fault handler can't be
found (triple fault).

Add a toolchain target spec for AArch64

Add an outline document for a port of the Redox kernel to the Arm AAr…

Also fix a typo with the device_crate URL.