Romanizes double vowels per the standard outlined in Hepburn Romanization.
Implemented in - Please use this instead of using this directly. It enforces subst for this *very* costly module.
Any double vowels will get converted to a long vowel, ou will get converted to ō.
{{#invoke:Hepburner|toHepburn|Kinou}} =>
{{#invoke:Hepburner|toHepburn|Ooki}} =>
{{#invoke:Hepburner|toHepburn|kara-age}} =>
{{#invoke:Hepburner|toHepburn|sakkaa}} =>
{{#invoke:Hepburner|toHepburn|raamen}} =>
{{#invoke:Hepburner|toHepburn|ヴィデオ}} =>
{{#invoke:Hepburner|toHepburn|いこう}} =>
{{#invoke:Hepburner|toHepburn|やった}} =>
{{#invoke:Hepburner|toHepburn|いきましょう}} =>
{{#invoke:Hepburner|toHepburn|ちゅうにびょう}} =>
{{#invoke:Hepburner|toHepburn|つづく}} =>
note: oU aA or the like will break it. You should never, ever, ever do this regardless, but note that is a limitation. If you need that, add it to the list, following the current pattern.