[bindings] Replace deprecated allow-none with optional and nullable

src/hb-blob.cc

diff --git a/src/hb-blob.cc b/src/hb-blob.cc
index d8b295e..51ea20d 100644
--- a/src/hb-blob.cc
+++ b/src/hb-blob.cc
@@ -82,8 +82,8 @@
  * @data: (array length=length) (element-type uint8_t) (closure user_data) (destroy destroy) (scope notified) (transfer none): Pointer to blob data.
  * @length: Length of @data in bytes.
  * @mode: Memory mode for @data.
- * @user_data: (allow-none): Data parameter to pass to @destroy.
- * @destroy: (allow-none): Callback to call when @data is not needed anymore.
+ * @user_data: (nullable): Data parameter to pass to @destroy.
+ * @destroy: (nullable): Callback to call when @data is not needed anymore.
  *
  * Creates a new "blob" object wrapping @data.  The @mode parameter is used
  * to negotiate ownership and lifecycle of @data.

src/hb-shape.cc

diff --git a/src/hb-shape.cc b/src/hb-shape.cc
index 100fb3c..9a59c08 100644
--- a/src/hb-shape.cc
+++ b/src/hb-shape.cc
@@ -200,7 +200,7 @@
  * hb_feature_from_string:
  * @str: (array length=len):
  * @len: 
- * @feature: (out) (allow-none):
+ * @feature: (out) (optional):
  *
  * 
  *

src/hb-unicode.cc

diff --git a/src/hb-unicode.cc b/src/hb-unicode.cc
index d59dfb2..fc19006 100644
--- a/src/hb-unicode.cc
+++ b/src/hb-unicode.cc
@@ -157,7 +157,7 @@
 
 /**
  * hb_unicode_funcs_create: (Xconstructor)
- * @parent: (allow-none):
+ * @parent: (nullable):
  *
  * 
  *