[docs] Change section titles again

I think I like the uniform "hb-*" more.
diff --git a/src/hb-face.cc b/src/hb-face.cc
index 2f6ccea..7ca4b1b 100644
--- a/src/hb-face.cc
+++ b/src/hb-face.cc
@@ -37,7 +37,7 @@
 
 /**
  * SECTION:hb-face
- * @title: hb_face_t
+ * @title: hb-face
  * @short_description: Font face objects
  * @include: hb.h
  *