Add base.token_reader to builtin.Types

lang/builtin/builtin.go

diff --git a/lang/builtin/builtin.go b/lang/builtin/builtin.go
index e604ff4..b4e9d7e 100644
--- a/lang/builtin/builtin.go
+++ b/lang/builtin/builtin.go
@@ -87,6 +87,7 @@
 
 	"io_reader",
 	"io_writer",
+	"token_reader",
 	"token_writer",
 
 	"frame_config",