Add more observances

[U-cauda-elongata]

Making a comprehensive of wildlife-related days is going to be a tough task, as there are a vast number of such days from highly orthodox ones like WWD (observed by UN) to relatively casual ones like World Raccoon Appreciation Day.

It would be great if there already is such a list suitable for our use case like UN's one (which is not quite comprehensive for our need). I'm not very optimistic about that possibility though.