p1: /v2/scrape, /v1/fetch, auth, CLI, contract tests

Single Fetcher.Fetch on the Guard that holds DenyPrefixes. skipTlsVerification
is ignored. No 502. keys add writes the secret only to --out. Release binary
has no -test-allow-prefix.

vendor/github.com/JohannesKaufmann/html-to-markdown/v2/converter/plugin.go

@@ -0,0 +1,22 @@
+package converter
+
+// Plugin can be used to extends functionality beyond what
+// is offered by commonmark.
+type Plugin interface {
+	// The public name of the plugin, e.g. "strikethrough"
+	Name() string
+
+	// Init is called to initialize the plugin. It can be used to
+	// *validate* the arguments and *register* the rules.
+	Init(conv *Converter) error
+}
+
+// WithPlugins can be used to add additional functionality to the converter.
+func WithPlugins(plugins ...Plugin) converterOption {
+	return func(c *Converter) error {
+		for _, plugin := range plugins {
+			c.Register.Plugin(plugin)
+		}
+		return nil
+	}
+}