markup/highlight: Add wrapperClass option

The need comes from Tailwind's typography plugin. There's currently no way to turn that off outside of the markup, see https://github.com/tailwindlabs/tailwindcss-typography/pull/363

markup/highlight/config.go

@@ -45,13 +45,18 @@ var DefaultConfig = Config{
 	NoClasses:          true,
 	LineNumbersInTable: true,
 	TabWidth:           4,
+	WrapperClass:       "highlight",
 }
 
 type Config struct {
 	Style string
 
+	// Enable syntax highlighting of fenced code blocks.
 	CodeFences bool
 
+	// The class or classes to use for the outermost element of the highlighted code.
+	WrapperClass string
+
 	// Use inline CSS styles.
 	NoClasses bool