Support for writing TEXT (tEXt) chunk in zune-png

[apps4uco]

Hi, my usecase is to write thumbnails according to https://specifications.freedesktop.org/thumbnail-spec/thumbnail-spec-latest.html. And Id like to use zune for that.

However from looking through the code it appears you dont currently support writing Text Chunks.

Do you have plans to support tEXt Textual data Chunks https://www.w3.org/TR/PNG-Chunks.html#C.tEXt ?

Are you open to a PR for this?

[etemesi254]

Hi, thanks for the issue. Yes I do eventually plan to support text segments, a PR would be welcome, but even before that I need to finalize the png encoder, specifically zlib data isn't compressed, so it leads to really big png images.

I can't say when I'll be done, this is just a side project for now and writing performant and safe code takes time, sometimes quite a long time..