Metadata to configure wildcard patterns

[simonw]

For configuring patterns, I'll go with this:

{
    "plugins": {
        "datasette-render-markdown": {
            "patterns": ["*_md"]
        }
    }
}

This supports multiple patterns. It also means you can disable wildcard column matching entirely with "patterns": [].

Originally posted by @simonw in #1 (comment)