Initial priority-based scheduler

- Scheduler now has multiple linked_lists of processes at different
  priorities
- Process structure improvements
- scheduler::tick() and scheduler::schedule() separation

src/kernel/loader.s

@@ -8,8 +8,14 @@ ramdisk_process_loader:
 	; create_process already pushed a cpu_state onto the stack for us, this
 	; acts both as the cpu_state parameter to load_process, and the saved
 	; state for the following iretq
+	;
+	; Additional parameters:
+	;  rax - the address of the program image
+	;  rbx - the size of the program image
+	;  rcx - the address of this process' process structure
 	mov rdi, rax
 	mov rsi, rbx
+	mov rdx, rcx
 	call load_process
 
 	pop_all_and_segments