[RFC] Japanese ruby font

[SuibianP]

I feel it is useful and feasible to have a font for Japanese ruby with the same GSUB mechanism. As a lot of the tooling would be similar, this could preferably be incorporated in this codebase. I am unfamiliar with GSUB implementation, but the chain of context substitutions might look like the following,

1. Match against special case table. This includes

   • 重箱/湯桶読み ex. 金色 手紙
   • Irregular readings, among other special cases ex. 山葵 早稲田 倶楽部
   • Common omitted okurigana ex. 売上 申込

2. Kun'yomi if the succeeding kana(s) match the expected conjugation context.

   Ex. For 炊 whose kJapanese field is スイ たく かしぐ, た is chosen if followed by ka-column or い.

3. Voiced on'yomi if the rendaku rules are satisfied.

   Ex. そく is voiced in 満足

4. Original on'yomi

The on'yomi and kun'yomi can be retrieved from the kJapanese[On|Kun]? Unicode Unihan database fields.

[SuibianP]

Another hard issue would be 見 verbs. It would be hard to tell the reading by rule 2 as the conjunctive form has no okurigana. (ex. 見逃して vs 見学して)