Add support for audio post downloading in Tumblr ripper

[virtualzx-nad]

Original issue: RipMeApp#2101

Problem:
The Tumblr ripper currently doesn't support downloading audio posts. This feature needs to be added to make the ripper more complete.

Requirements:

1. Add audio post detection to TumblrRipper
2. Implement audio file downloading
3. Handle different audio formats
4. Add appropriate error handling
5. Include tests
6. Update documentation

Difficulty: Moderate
Type: Feature