Add User defined text information frame

[chicio]

Add support for the TXXX comment frame.

Describe the solution you'd like
Add support for the TXXX comment frame. This frame has the same structure of USTL and COMM unsynchronised lyrics.
This issue should be done after #46 is completed.
I need to:

• use the same approach used for USTL and COMM frame to add the TXXX frame

See chain of creation and parsing in ID3TagEditor
https://id3.org/d3v2.3.0 see section "4.2.2. User defined text information frame"

[KrLite]

Hi! Is there any progress on implementing TXXX frames?

[chicio]

Hi @KrLite , still not in progress (I'm focused on other side projects right now). Do you want to give it a try and implement this feature whenever you have some free time? This will be so helpful to make the project move forward and have new/addition features?

[KrLite]

I'm willing to contribute!
This library almost fits my needs except lacking the ability to handle user defined information frames. However, most of the other Swift packages targeting ID3 tagging are even more under-featured. I always wanted a feature-to-feature Swift layer for TagLib, but nobody is making that 🥲.

[chicio]

If you want to give it a try you can check how the COMM and USLT frames are implemented. TXXX should be similar (only the language field in the header is not present, but the description ($00 terminated) + content should be generated in the same way).