this is not exactly great, but it should be "good enough"
note that the new `group` function should not escape in the wild, as
we don't document it and only use it internally
I tried using `$[scale foo bar]` instead of `$[group foo bar]`, but
that would be rendered as `<i>foo bar</i>` when sent over the network
to non-misskey instances, and we don't want that
This fix makes `MfmService.fromHtml()` method accept `<ruby>` tags
and translate it to MFM's ruby characters syntax (`$[ruby ...]`).
このパッチは`MfmService.fromHtml()`メソッドが`<ruby>`タグをMFMの
読み仮名（ルビ）文法に翻訳する様に修正します。
* chore: Add the SPDX information to each file
Add copyright and licensing information as defined in version 3.0 of
the REUSE Specification.
* tweak format
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Co-authored-by: syuilo <Syuilotan@yahoo.co.jp>
