added model loading from ckpt

tools/demo_api.py

@@ -133,6 +133,12 @@ def build_predictor(
     model.eval()
     logger.info("Model Summary: {}".format(get_model_info(model, exp.test_size)))
 
+    logger.info("loading checkpoint")
+    ckpt = torch.load(ckpt_path, map_location="cpu")
+    # load the model state dict
+    model.load_state_dict(ckpt["model"])
+    logger.info("loaded checkpoint done.")
+    
     predictor = Predictor(
         model, exp, COCO_CLASSES,
         None, decoder=None,