The short answer? You can’t do it without plugins.
The long answer? Well, in GitHub pages history of times past, you
would have been able to use the redcarpet Markdown parser that you
could then configure an autolink plugin, and Voila! It would just
work. Nowadays you can’t do that anymore since Kramdown is now the
only supported Markdown parser on GitHub Pages.
And unfortunately, it appears the only easy way to get this working with Kramdown is through the use of a plugin, which isn’t as convenient on GitHub pages.
20180528/DuckDuckGo jekyll markdown flavor
20180528/https://stackoverflow.com/questions/13464590/github-flavored-markdown-and-pygments-highlighting-in-jekyll#13614020
20180528/https://github.com/nono/Jekyll-plugins
20180528/https://github.com/vmg/redcarpet
20180528/https://jekyllrb.com/docs/plugins/
20180528/https://jekyllrb.com/docs/configuration/
20180528/https://help.github.com/articles/updating-your-markdown-processor-to-kramdown/
20180528/https://kramdown.gettalong.org/documentation.html
20180528/https://kramdown.gettalong.org/quickref.html
20180528/https://kramdown.gettalong.org/rdoc/index.html
20180528/https://kramdown.gettalong.org/rdoc/Kramdown/Document.html
20180528/https://kramdown.gettalong.org/rdoc/Kramdown/Options.html
20180528/DuckDuckGo kramdown auto links url
20180528/https://github.com/shoyan/kramdown_easy_link
Now, the updated state-of-the-art situation of math on the web.
What’s going on with this new KaTeX? Basically, it’s a MathML
generator, rather than a solution that eschews on MathML. Yeah, so
just like blahtex/blahtexml 10 years ago, only more popular this
time through. It’s main claim is that it is faster than MathJax.
SsKaTeX runs server-side, but it is not recommended to be used with
untrusted code.
20180528/https://kramdown.gettalong.org/math_engine/mathjax.html
20180528/https://khan.github.io/KaTeX/
20180528/https://kramdown.gettalong.org/math_engine/sskatex.html