Introducing Tail Clouds v0.21.1

This is just a minor update for v0.21.1

I noticed that tornado funnels were rendering through the wall clouds, so this patches the wall cloud rendering so that hopefully doesn't happen anymore (it will by design for mega-wedges as the tornado funnel absorbs the wall cloud as part of its transition into a mega-wedge).

While fixing wall clouds I decided to have a first attempt at adding tail clouds, they are somewhat noticeable but pretty small so I will be improving them for the next update.