Complete second logic pass, remove underscore from package name

reolinkapi/download.py

@@ -0,0 +1,18 @@
+class DownloadAPIMixin:
+    """API calls for downloading video files."""
+    def get_file(self, filename: str, output_path: str) -> bool:
+        """
+        Download the selected video file
+        :return: response json
+        """
+        body = [
+            {
+                "cmd": "Download",
+                "source": filename,
+                "output": filename,
+                "filepath": output_path
+            }
+        ]
+        resp = self._execute_command('Download', body)
+
+        return resp