free task page dir.
add ls, get_cursor_pos, set_cursor_pos, set_term_color system call.
add new_pages() and remove_pages() system call, no test yet!
system call new_pages() and remove_pages()
add get_ticks() system call.
add sleep() system call.
add spinlock when remove or add to thread list.
make global variable in thread.c static.
add yield() system call.