Tag Alias: prone -> on_stomach

Aliasing prone -> on_stomach.
Aliasing supine -> on_back.

Reason: I've seen 'prone' used before, and (possibly as a result) 9twas my first choice of search word when looking for the tag. I would assume the same could happen with someone else with on_back in mind looking for supine.

Note that if I've accidentally confused 'to' and 'from' again, then consider 'Reason' as: 'it's shorter and less likely to confuse.' instead.

Well, prone is shorter, but I'd say on_stomach is less likely to confuse. +1 for aliasing to on_stomach.

+1 from me as well. "Prone" is the technical term, yes, but an alias will keep it useful anyway.

Done the aliases, to the on_* tags.