Extra Markdown extensions

Since version 0.126.0 Hugo offers to render additional inline markup for super- and subscripts, insertions, and marked content.

When we like to write 1^st, H₂O, marked, or inserted content we can achieve this with extended Goldmark markup:

1^st^, H~2~O, ==marked==, or ++inserted content++

The necessary configuration options for these new markup extensions are described in the Hugo documentation and can be enabled separately.

The extensions are part of Hugo’s goldmark extensions. Thanks a lot to BEP and Joe Mooring for their implementation suggestions, the integration, and some code improvements.