Support AsciiDoc files

[DanielSWolf]

AsciiDoc files (extension: .adoc) are currently rendered as plain text. It would be great if github1s supported syntax highlighting (and possibly preview, too) of AsciiDoc files, the way it already supports Markdown files.

[welcome[bot]]

Hello there!👋 Welcome to the project!💖 Thank you and congrats🎉for opening your very first issue in this project.Be patient while we get back to you.😄

[conwnet]

We can migrate the AsciiDoc extension to support it as before, but we are trying to find a more common way to do this. If there is any progress, I will explain it here. Thanks for your advice~❤️