Rename some functions so they are less awkward

* Note that the conversion of slist_pop* to dlist_pop* are opposite

	* dlist_push -> dlist_pushfront
	* dlist_append -> dlist_pushback
	* dlist_pop -> dlist_popback
	* dlist_dequeue -> dlist_popfront

	* slist_push -> slist_pushfront
	* slist_append -> slist_pushback
	* slist_pop -> slist_popfront
	* slist_dequeue -> slist_popback