See <https://akkoma.dev/AkkomaGang/akkoma/issues/381>
We can't use the HTML content as-is.
[FEP-c16b](https://codeberg.org/fediverse/fep/src/branch/main/fep/c16b/fep-c16b.md) was
written to have a "scrubber friendly" way of representing MFM functions in HTML. Here
we add support in the backend for the functions Foundkey supports. The front-ends then
needs to add support to make sure the HTML representation is turned into a correct view.
(I.e. by help of CSS and Javascript)
FEP-c16b also has a discovery mechanism to indicate to recieving servers that they can
use the `content` directly. This is not implemented in this commit
This allows to format Japanese furigana (aka ruby) notation.
Present in XHTML 1.1, HTML 5 and later. Absent in XHTML 1.0, HTML 4 and earlier.
See https://www.w3.org/TR/ruby/
