fs/config: add header-download and header-upload flags

fs/config.go

@@ -111,6 +111,8 @@ type ConfigInfo struct {
 	MultiThreadStreams     int
 	MultiThreadSet         bool   // whether MultiThreadStreams was set (set in fs/config/configflags)
 	OrderBy                string // instructions on how to order the transfer
+	UploadHeaders          []*HTTPOption
+	DownloadHeaders        []*HTTPOption
 }
 
 // NewConfig creates a new config with everything set to the default