Add support for config param summary-tags

This parameter can be used to specify max number of tags to show on
the summary page. If not specified, all tags are printed.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -143,6 +143,7 @@ extern int cgit_cache_dynamic_ttl;
 extern int cgit_cache_static_ttl;
 extern int cgit_cache_max_create_time;
 extern int cgit_summary_log;
+extern int cgit_summary_tags;
 
 extern int cgit_max_msg_len;
 extern int cgit_max_repodesc_len;