[PATCH 1/3] windowscodecs: Add initial implementation of the GIF encoder.

[Esme Povirk (they/them)]

> It's my own development, but for a different target. I was using the LZW
> encoder with a specially crafted tool, and after that adapted it for GIF.
> If really necessary user_write() callback could be removed.

OK. I don't see a need to change it, it just made me wonder where the
code came from.

> > If possible, I would prefer not to maintain an implementation of LZW
> > compression.
>
> Why? It's plain and simple. In comparison LZW decoder is more complicated,
> but we have it included.

That was before my time, I just moved it from the old olepicture code.
I don't know what the rationale was for importing gif decompression
code.

Surprisingly, I can't find a library we could use for LZW compression,
so maybe we do need to include it. We could add a dependency on a gif
library, but that doesn't seem worth it to me.