[HB] Rename _duplicate to _copy

To be in line with cairo
diff --git a/src/hb-font.c b/src/hb-font.c
index 078a3bc..2397d77 100644
--- a/src/hb-font.c
+++ b/src/hb-font.c
@@ -77,7 +77,7 @@
 }
 
 hb_font_callbacks_t *
-hb_font_callbacks_duplicate (hb_font_callbacks_t *other_fcallbacks)
+hb_font_callbacks_copy (hb_font_callbacks_t *other_fcallbacks)
 {
   hb_font_callbacks_t *fcallbacks;
 
@@ -141,7 +141,7 @@
 }
 
 hb_unicode_callbacks_t *
-hb_unicode_callbacks_duplicate (hb_unicode_callbacks_t *other_ucallbacks)
+hb_unicode_callbacks_copy (hb_unicode_callbacks_t *other_ucallbacks)
 {
   hb_unicode_callbacks_t *ucallbacks;
 
diff --git a/src/hb-font.h b/src/hb-font.h
index e563fa7..deab22e 100644
--- a/src/hb-font.h
+++ b/src/hb-font.h
@@ -58,7 +58,7 @@
 hb_font_callbacks_destroy (hb_font_callbacks_t *fcallbacks);
 
 hb_font_callbacks_t *
-hb_font_callbacks_duplicate (hb_font_callbacks_t *fcallbacks);
+hb_font_callbacks_copy (hb_font_callbacks_t *fcallbacks);
 
 /*
 
@@ -98,7 +98,7 @@
 hb_unicode_callbacks_destroy (hb_unicode_callbacks_t *ucallbacks);
 
 hb_unicode_callbacks_t *
-hb_unicode_callbacks_duplicate (hb_unicode_callbacks_t *ucallbacks);
+hb_unicode_callbacks_copy (hb_unicode_callbacks_t *ucallbacks);
 
 /*