Code refactoring

- Code refactoring
- Fix a bug that the other player will not become the host of the room at once, when the player disconnect in link play.

> Maybe add many unknown bugs. XD
> The song database `arcsong.db` will not used in the future. You can use a tool in `tool` folder to import old data.

latest version/core/util.py

@@ -0,0 +1,27 @@
+import hashlib
+import os
+
+
+def md5(code):
+    # md5加密算法
+    code = code.encode()
+    md5s = hashlib.md5()
+    md5s.update(code)
+    codes = md5s.hexdigest()
+
+    return codes
+
+
+def get_file_md5(file_path):
+    # 计算文件MD5
+    if not os.path.isfile(file_path):
+        return None
+    myhash = hashlib.md5()
+    with open(file_path, 'rb') as f:
+        while True:
+            b = f.read(8096)
+            if not b:
+                break
+            myhash.update(b)
+
+    return myhash.hexdigest()