Add license file and copyright notices

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

cache.c

@@ -1,3 +1,11 @@
+/* cache.c: cache management
+ *
+ * Copyright (C) 2006 Lars Hjemli
+ *
+ * Licensed under GNU General Public License v2
+ *   (see COPYING for full license text)
+ */
+
 #include "cgit.h"
 
 const int NOLOCK = -1;