Add support for 'project-list' option

This option specifies the location of a projectlist file as used by
gitweb - when 'scan-tree' is later specified, only the projects listed in
the projectlist file will be added.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -166,6 +166,7 @@ struct cgit_config {
 	char *logo;
 	char *logo_link;
 	char *module_link;
+	char *project_list;
 	char *robots;
 	char *root_title;
 	char *root_desc;