made popping with lists work. yay! (also new demo to show the thing)

src/list.c

@@ -106,3 +106,15 @@ listCleanup(list_t* l) {
     vectorCleanup((vector_t *)l->data);
     free(l);
 }
+
+void*
+listPop(list_t* l) {
+    vector_t *first_ptr = (vector_t *)vectorPop((vector_t *)l->data);
+    void *ptr = vectorPop(first_ptr);
+    l->size -= 1;
+
+    if (l->size <= l->capacity / 2) l->capacity /= 2;
+    if (l->capacity == 0) l->capacity = 1;
+
+    return ptr;
+}