No header flags supported

[rstemmer]

Flags to implement:

• ID3v2.3.0
  • a - Unsynchronisation
  • b - Extended header (read/write)
  • c - Experimental indicator
• ID3v2.4.0
  • a - Unsynchronisation
  • b - Extended header (read/write)
  • c - Experimental indicator
  • d - Footer present

[rstemmer]

This is no longer a real limitation.
Most common flags are supported.