feat(queue): introduce a queue ds, internally this is just a stack...

the only actual difference is a oneline change which makes pushing
append instead of prepend the new data.

ds.h

@@ -27,6 +27,8 @@ typedef struct {
   ds_sll_t *items;
 } ds_stack_t;
 
+typedef ds_stack_t ds_queue_t;
+
 #define ds_ll_foreach(t, ll) for (t *cur = ll; cur; cur = cur->next)
 
 /**
@@ -206,4 +208,37 @@ void *ds_stack_pop(ds_stack_t *stack);
  */
 void *ds_stack_peek(ds_stack_t *stack, unsigned x);
 
+/**
+ * @brief initialize a new queue
+ *
+ * @return the queue
+ */
+ds_queue_t *ds_queue_init(void);
+
+/**
+ * @brief push new data onto the queue
+ *
+ * @param queue the queue
+ * @param data the data
+ * @return 0 on success
+ */
+int ds_queue_push(ds_queue_t *queue, void *data);
+
+/**
+ * @brief pop the data off the top of the queue
+ *
+ * @param queue the queue
+ * @return the data
+ */
+void *ds_queue_pop(ds_queue_t *queue);
+
+/**
+ * @brief peek forward x items
+ *
+ * @param queue the queue
+ * @param x how many items to look ahead
+ * @return the data or NULL if out of range
+ */
+void *ds_queue_peek(ds_queue_t *queue, unsigned x);
+
 #endif