Add support for 'noheader' option

This option can be used to disable the standard cgit page header, which
might be useful in combination with the 'embedded' option.

Suggested-by: Mark Constable <markc@renta.net>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -172,6 +172,7 @@ struct cgit_config {
 	int summary_log;
 	int summary_tags;
 	int embedded;
+	int noheader;
 };
 
 struct cgit_page {