Add lm decode for the Python API. (#353)

* Add lm decode for the Python API.

* fix style.

* Fix LogAdd,

	Shouldn't double lm_log_prob when merge same prefix path

* sort the import alphabetically

python-api-examples/online-decode-files.py

@@ -115,6 +115,24 @@ def get_args():
         """,
     )
 
+    parser.add_argument(
+        "--lm",
+        type=str,
+        default="",
+        help="""Used only when --decoding-method is modified_beam_search.
+        path of language model.
+        """,
+    )
+
+    parser.add_argument(
+        "--lm-scale",
+        type=float,
+        default=0.1,
+        help="""Used only when --decoding-method is modified_beam_search.
+        scale of language model.
+        """,
+    )
+
     parser.add_argument(
         "--provider",
         type=str,
@@ -215,6 +233,8 @@ def main():
             feature_dim=80,
             decoding_method=args.decoding_method,
             max_active_paths=args.max_active_paths,
+            lm=args.lm,
+            lm_scale=args.lm_scale,
             hotwords_file=args.hotwords_file,
             hotwords_score=args.hotwords_score,
         )