Add hb_feature_to/from_string()
diff --git a/src/hb-common.cc b/src/hb-common.cc
index 1301ab2..33a514d 100644
--- a/src/hb-common.cc
+++ b/src/hb-common.cc
@@ -58,6 +58,15 @@
   return HB_TAG_CHAR4 (tag);
 }
 
+void
+hb_tag_to_string (hb_tag_t tag, char *buf)
+{
+  buf[0] = (char) (uint8_t) (tag >> 24);
+  buf[1] = (char) (uint8_t) (tag >> 16);
+  buf[2] = (char) (uint8_t) (tag >>  8);
+  buf[3] = (char) (uint8_t) (tag >>  0);
+}
+
 
 /* hb_direction_t */