Meta-data system

[p0nce]

• study what FreeImage does => it implements iterators that avoid to read the whole metadata if not needed, apparently it does not parse metadata preemptively. Can represent unknown type. I don't really like all this.
• study what https://github.com/DlangGraphicsWG/image/blob/master/src/wg/image/metadata.d does => linked-list of arena-based metadata, quite short and cool (yes), based by templated type instead of UUID (meh)
• similar system to mallocArea, metadata is owned when data is owned?
• (optional) each layer should be able to have meta-data (eg: GIF frame times)
  • alternatively, each layer has access only to global metadata? (no layer-specific metadata)
• (optional) layered views also points in layered metadata, so that you can create multi-layered views, with access to layer metadata, without reallocation