To Do ----- * Add support for more embedded thumbnail formats. Right now, nsxiv seems to use the smallest one. [Issue #238](https://github.com/muennich/sxiv/issues/238). * Load all frames from TIFF files. We have to write our own loader for this to happen--just like we did for GIF images--because Imlib2 does not support multiple frames. [Issue #241](https://github.com/muennich/sxiv/issues/241).