Add map_pop to remove the last element from an array-like map.

src/object.c

@@ -547,6 +547,15 @@ oop map_append(oop map, oop value)
     return map_set(map, makeInteger(map_size(map)), value);
 }
 
+oop map_pop(oop map)
+{                                                                   assert(map_isArray(map));
+    size_t size = get(map, Map, size);
+    if (size == 0) return null;
+    oop val = get(map, Map, elements)[--size].value;
+    set(map, Map, size, size);
+    return val;
+}
+
 oop makeArrayFromElement(oop elem, int repeat)
 {
     oop array= makeMapCapacity(repeat);