basic hr support

docs/honk.5

@@ -62,6 +62,10 @@ URLs beginning with
 or
 .Dq https
 will be autolinked.
+.It rules
+Exactly three dashes on a line,
+.Dq --- ,
+will become a horizontal rule.
 .El
 .Pp
 If the first line of a honk begins with

markitzero.go

@@ -78,6 +78,7 @@ func markitzero(s string) string {
 	s = re_bolder.ReplaceAllString(s, "$1<b>$2</b>$3")
 	s = re_italicer.ReplaceAllString(s, "$1<i>$2</i>$3")
 	s = re_quoter.ReplaceAllString(s, "<blockquote>$1</blockquote><p>")
+	s = strings.Replace(s, "\n---\n", "<hr><p>", -1)
 
 	s = re_lister.ReplaceAllStringFunc(s, func(m string) string {
 		m = strings.Trim(m, "\n")