shipmare -> ship pony

Merge shipmare and battleship ponies into ship pony and change to a race (and imply original species). Consider adding the description of “anthropomorphised naval ships”, so as not to be confused with spaceship ponies.

The problem is that they both seems to be referring to different things. “ship ponies” seem more… mechanical than the ones in the “shipmare” tag.

@Mildgyth
Hm, yeah, I suppose that’s true. Generally I’m in favour of consolidating small tags for the sake of improved search results–you wouldn’t want to search for ‘shipmare’ and miss out on the ‘ship ponies’ due to a technicality, or search for ‘ship pony’ and think there are only six ponified ships. If we’re being picky, those six are more ‘pony ships’ than ‘ship ponies’. But I have no stake in the decision either way; if it’s not redundant to you, that’s fine.