object: add b_list object

b_list behaves exactly like b_queue, with two key differences:

  1) it is memory-managed like other b_objects, which means it
     is stored on the heap and ref-counted.
  2) it is not an invasive data structure, and will automatically
     create and manage list nodes that contain pointers to the
     list items.

object/list.h

@@ -0,0 +1,19 @@
+#ifndef _BLUELIB_LIST_H_
+#define _BLUELIB_LIST_H_
+
+#include "object.h"
+
+#include <blue/core/queue.h>
+
+struct b_list {
+	struct b_object l_base;
+	struct b_queue l_queue;
+	size_t l_len;
+};
+
+struct b_list_entry {
+	struct b_queue_entry e_entry;
+	void *e_data;
+};
+
+#endif