Doc: Replace the deprecated highlightlang directive by highlight. (#13377)

highlightlang is deprecated since April 2018 in Sphinx.
See https://github.com/sphinx-doc/sphinx/pull/4845
diff --git a/Doc/extending/building.rst b/Doc/extending/building.rst
index 9bfad7f..753b551 100644
--- a/Doc/extending/building.rst
+++ b/Doc/extending/building.rst
@@ -1,4 +1,4 @@
-.. highlightlang:: c
+.. highlight:: c
 
 .. _building:
 
@@ -20,7 +20,7 @@
 It returns either a fully-initialized module, or a :c:type:`PyModuleDef`
 instance. See :ref:`initializing-modules` for details.
 
-.. highlightlang:: python
+.. highlight:: python
 
 For modules with ASCII-only names, the function must be named
 ``PyInit_<modulename>``, with ``<modulename>`` replaced by the name of the
@@ -43,7 +43,7 @@
 See the *"Multiple modules in one library"* section in :pep:`489` for details.
 
 
-.. highlightlang:: c
+.. highlight:: c
 
 Building C and C++ Extensions with distutils
 ============================================
diff --git a/Doc/extending/embedding.rst b/Doc/extending/embedding.rst
index 13d83b7..483bc85 100644
--- a/Doc/extending/embedding.rst
+++ b/Doc/extending/embedding.rst
@@ -1,4 +1,4 @@
-.. highlightlang:: c
+.. highlight:: c
 
 
 .. _embedding:
diff --git a/Doc/extending/extending.rst b/Doc/extending/extending.rst
index 433178a..e459514 100644
--- a/Doc/extending/extending.rst
+++ b/Doc/extending/extending.rst
@@ -1,4 +1,4 @@
-.. highlightlang:: c
+.. highlight:: c
 
 
 .. _extending-intro:
diff --git a/Doc/extending/newtypes.rst b/Doc/extending/newtypes.rst
index 8b9549d..308c067 100644
--- a/Doc/extending/newtypes.rst
+++ b/Doc/extending/newtypes.rst
@@ -1,4 +1,4 @@
-.. highlightlang:: c
+.. highlight:: c
 
 .. _new-types-topics:
 
diff --git a/Doc/extending/newtypes_tutorial.rst b/Doc/extending/newtypes_tutorial.rst
index b4bf9b9..59c8cc0 100644
--- a/Doc/extending/newtypes_tutorial.rst
+++ b/Doc/extending/newtypes_tutorial.rst
@@ -1,4 +1,4 @@
-.. highlightlang:: c
+.. highlight:: c
 
 .. _defining-new-types:
 
diff --git a/Doc/extending/windows.rst b/Doc/extending/windows.rst
index 67bdd47..c7b92c6 100644
--- a/Doc/extending/windows.rst
+++ b/Doc/extending/windows.rst
@@ -1,4 +1,4 @@
-.. highlightlang:: c
+.. highlight:: c
 
 
 .. _building-on-windows: