modularize src

+ merge main.py and manage.py
+ move start logic to swingmusic/__main__.py
+ add a run.py on the project root

swingmusic/utils/files.py

@@ -0,0 +1,21 @@
+import mimetypes
+
+
+def get_mime_from_ext(filename: str):
+    """
+    Constructs a mime type from a file extension.
+    """
+    ext = filename.rsplit(".", maxsplit=1)[-1]
+    return f"audio/{ext}"
+
+
+def guess_mime_type(filename: str):
+    """
+    Guess the mime type of a file.
+    """
+    type = mimetypes.guess_type(filename)[0]
+
+    if type is None:
+        return get_mime_from_ext(filename)
+
+    return type