Replace webp library

[jm-francis]

Hello, I suggest you check out gen2brain/webp, it's a CGO-free webp library which I have tested, and I found it provides very similar performance and quality to kolesa-team webp, which I was using before in my project.

[tdewolff]

I believe that version adds a huge size to your binaries, but I'm not sure. I'm not a fan of the WASM replacement, but perhaps we could use a purego version that is only available if you have the shared libraries (.so or .dll) available? It is true that the Go version is very slow in comparison.