Add skeleton for yield system call.
Use memory barrier in ioapic_read/write.
Use memory barrier in AP boot code.
Update TODO list.
Remove most of the GRUB bug info - 2.00 has been out for a while.
Rename tty trace implementation to vga.
Split intr_depth as it was really used for two distinct purposes.
Rename intr_state_t to cpu_state_t, and move it to a new header.
Add reserved interrupt number for cpu_state_save().
Sketch out how sys_yield() could work.
Update TODO list.
Fix #includes.
Update TODO list again.
Merge branch 'barrier'