Allow for streaming write into `gif-encoder`

[twolfson]

As inspired by the pngjs API, we should allow streaming in of rgba values. I am curious how we will make pipe out work sans methods though.

[twolfson]

We will probably change the API so it is impllicit over imperative. When we pipe, we will automatically add header and footer bytes.

There will still be an add frame method. There will also be a frame event for mutation before we mutate into the color pallette. In fact, we should have a color palette event and the ability to skip over recalculating that per frame (e.g. it never changed, we were just optimizing calculations in gifsockets)