Support for converting values to GIFs

[jackfirth]

I'd like to write some documentation with example code that includes embedded animations. I assumed I'd be able to do this by making the animations implement the prop:convertible interface and support conversion to GIFs. But according to the docs for render-convertible-as, it looks like only the PNG and SVG formats are supported. Is GIF support reasonable?

[spdegabrielle]

I think this would be a valuable addition. Being able to include animations created with the record?(2htdp/universe) sounds like it would provide a nice way to enhance the documentation.