Without extension, Visual Studio Code "auto detect" mistakes AsciiDoc for Markdown

[hickford]

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Assuming you don't have the AsciiDoctor extension installed, Visual Studio Code's "auto detect" feature mistakes AsciiDoc for Markdown, even if it has the file extension .adoc.

This is a bug in upstream Visual Studio Code, but it's relevant to this project because it makes this extension harder to discover for Visual Studio Code users.