Add clear function that clears the linked list.

include/ll.h

@@ -109,5 +109,12 @@ void* ll_pophead(ll* ll);
  */
 void* ll_poptail(ll* ll);
 
+/**
+ * Removes all elements from the list, freeing the underlying memory
+ * but keeping the data intact,
+ * @param ll the linked list to clear.
+ */
+void ll_clear(ll* ll);
+
 
 #endif

src/ll.c

@@ -113,3 +113,14 @@ void* ll_poptail(ll* ll) {
   }
   return to_return;
 }
+
+void ll_clear(ll* ll){
+  ll_node* head = ll->head;
+  while(ll->head){
+    ll_node* to_free = head;
+    head = head->next;
+    free(to_free);
+  }
+  ll->head = NULL;
+  ll->tail = NULL;
+}