Make source more digestable for gobject-introspection

src/hb-blob.cc

diff --git a/src/hb-blob.cc b/src/hb-blob.cc
index 3cc2d9d..b6e696b 100644
--- a/src/hb-blob.cc
+++ b/src/hb-blob.cc
@@ -46,7 +46,7 @@
 #endif
 
 
-struct _hb_blob_t {
+struct hb_blob_t {
   hb_object_header_t header;
   ASSERT_POD ();