Added Documentation and minor tweaks

[yakuraku]

Change Log:

1. Added comments to explain the purpose of each function and section of the code. Additionally, I've optimized the code by organizing it into functions and removing redundant code.
2. When adding music to the playlist, the code now checks for .mp3 and .wav file extensions explicitly.
3. The code for the GIF animation has been improved by encapsulating it in a function (update) and using a loop index (ind) to cycle through frames. This reduces code duplication and improves maintainability.