No frame flags supported

[rstemmer]

I never saw a frame that had any flags set. This issue just documents the missing support.

In case it becomes an issue, feel free to leave a comment.

Flags to implement:

• ID3v2.3.0
  • [ ] a - Tag alter preservation
  • [ ] b - File alter preservation
  • [ ] c - Read only
  • [ ] i - Compression
  • [ ] j - Encryption
  • [ ] k - Grouping identity
• ID3v2.4.0
  • [ ] a - Tag alter preservation
  • [ ] b - File alter preservation
  • [ ] c - Read only
  • [ ] h - Grouping identity
  • [ ] k - Compression
  • [ ] m - Encryption
  • [ ] n - Unsynchronisation
  • [ ] p - Data length indicator