Fixed hyperlinks

pervious commits were missing a _doc header

:ref: doc_guide instead of guide

development/cpp/custom_audiostreams.rst

@@ -1,4 +1,4 @@
-.. _custom_audiostreams:
+.. _doc_custom_audiostreams:
 
 Custom AudioStreams
 ===================

development/cpp/custom_godot_servers.rst

@@ -1,4 +1,4 @@
-.. _custom_godot_servers:
+.. _doc_custom_godot_servers:
 
 Custom Godot Servers
 ====================

development/cpp/custom_resource_format_loaders.rst

@@ -1,4 +1,4 @@
-.. _custom_resource_format_loaders:
+.. _doc_custom_resource_format_loaders:
 
 Custom Resource Format Loaders
 ==============================