[Tagging] re-write of wiki page for hitching animals

[Anne-Karoline Distel]

https://wiki.openstreetmap.org/wiki/Tag:amenity%3Danimal_hitch

I've also added a suggestion for rendering. The knot is by no means
correct for hitching animals to anything, but I struggled enough with
the paths there. I'm also not sure about the colour scheme; I went with
the "parking blue", but maybe amenities have a different colour.

Thanks, everyone, for their contribution to the discussion!

Anne