Feature request: add support for uncompressed frames

[pirey0]

Hey there, I've been using the library for a few days now and it's very useful, thank you for making and supporting it!

I'm using it to export ingame runs in gif format but I noticed that the LZW compression is, at times, too slow for my use case. I've read on Wikipedia that there's a way to abuse the LCW CLEAR instruction to add uncompressed frames. I've been trying to implement it myself but had no luck as of yet. Maybe someone with more experience on the matter has some insights or can help out?

It would be a very useful feature to generate Gifs at runtime.