Since 0.14, Hugo has defined a new concept called external helpers. It means that you can write your content using Asciidoc[tor], reStructuredText or Org-Mode. If you have files with associated extensions (details), then Hugo will call external commands to generate the content (the exception being Org-Mode content, which is parsed natively).
This means that you will have to install the associated tool on your machine to be able to use those formats.
For example, for Asciidoc files, Hugo will try to call asciidoctor or asciidoc command.
To use those formats, just use the standard extension and the front matter exactly as you would do with natively supported .md files.
Notes:
- as these are external commands, generation performance for that content will heavily depend on the performance of those external tools.
- this feature is still in early stage, hence feedback is even more welcome.