Class documentation doesn't show `prepend`ed classes

[gettalong]

The class documentation does have code to identify included and extended classes. However, prepended classes are not shown. See for example https://hexapdf.gettalong.org/documentation/reference/api/HexaPDF/Encryption/FastAES.html and https://github.com/gettalong/hexapdf/blob/master/lib/hexapdf/encryption/fast_aes.rb#L54