MarkdownBear: Verify the config_file

If the config_file is provided, all other options are ignored.

Closes #925

bears/markdown/MarkdownBear.py

@@ -101,7 +101,10 @@ def create_arguments(filename, file, config_file,
             "ruleRepetition": markdown_horizontal_rule_repeat,  # int
         }
 
-        config_json = json.dumps(remark_configs)
-        # Remove { and } as remark adds them on its own
-        settings = config_json[1:-1]
-        return '--no-color', '--quiet', '--setting', settings
+        if config_file:
+            return '--no-color', '--quiet', '--setting', config_file
+        else:
+            config_json = json.dumps(remark_configs)
+            # Remove { and } as remark adds them on its own
+            settings = config_json[1:-1]
+            return '--no-color', '--quiet', '--setting', settings