If no language is provided to Pygments, then try and guess it

Previously if no language was specified, then illegal args would be passed to pygments, for example `pygments -l -fhtml`, which would result in pygments printing an error.

helpers/pygments.go

@@ -94,7 +94,14 @@ func Highlight(code, lang, optsStr string) string {
 	var out bytes.Buffer
 	var stderr bytes.Buffer
 
-	cmd := exec.Command(pygmentsBin, "-l"+lang, "-fhtml", "-O", options)
+	var langOpt string
+	if lang == "" {
+		langOpt = "-g" // Try guessing the language
+	} else {
+		langOpt = "-l"+lang
+	}
+
+	cmd := exec.Command(pygmentsBin, langOpt, "-fhtml", "-O", options)
 	cmd.Stdin = strings.NewReader(code)
 	cmd.Stdout = &out
 	cmd.Stderr = &stderr