Add a pager on the repolist

This enables a pager on the repolist which restricts the number of entries
displayed per page, controlled by the new option `max-repo-count` (default
value 50).

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

cgit.h

@@ -145,6 +145,7 @@ struct cgit_config {
 	int enable_index_links;
 	int enable_log_filecount;
 	int enable_log_linecount;
+	int max_repo_count;
 	int max_commit_count;
 	int max_lock_attempts;
 	int max_msg_len;