kmalloc: add actual memory allocator

Now that memory allocation finally kind of works,
we can finally start focusing on the core system
architecture.  This commit also fixes some bugs in
get_page() and friends, as well as performance
improvements because the page map is addressed as
unsigned longs rather than individual bytes.

kernel/clist.c

@@ -18,7 +18,7 @@ void clist_add(struct clist *head, struct clist *new)
 	head->next = new;
 }
 
-void clist_add_end(struct clist *head, struct clist *new)
+void clist_add_first(struct clist *head, struct clist *new)
 {
 	head->prev->next = new;
 	new->next = head;