Issue #28755: Merge Arg Clinic howto from 3.6

Doc/howto/clinic.rst

+.. highlightlang:: c
+
 **********************
 Argument Clinic How-To
 **********************
@@ -78,17 +80,23 @@ Basic Concepts And Usage
 ========================
 
 Argument Clinic ships with CPython; you'll find it in ``Tools/clinic/clinic.py``.
-If you run that script, specifying a C file as an argument::
+If you run that script, specifying a C file as an argument:
+
+.. code-block:: shell-session
 
-    % python3 Tools/clinic/clinic.py foo.c
+    $ python3 Tools/clinic/clinic.py foo.c
 
 Argument Clinic will scan over the file looking for lines that
-look exactly like this::
+look exactly like this:
+
+.. code-block:: none
 
     /*[clinic input]
 
 When it finds one, it reads everything up to a line that looks
-exactly like this::
+exactly like this:
+
+.. code-block:: none
 
     [clinic start generated code]*/
 
@@ -99,7 +107,9 @@ lines, are collectively called an Argument Clinic "block".
 When Argument Clinic parses one of these blocks, it
 generates output.  This output is rewritten into the C file
 immediately after the block, followed by a comment containing a checksum.
-The Argument Clinic block now looks like this::
+The Argument Clinic block now looks like this:
+
+.. code-block:: none
 
     /*[clinic input]
     ... clinic input goes here ...
@@ -378,9 +388,7 @@ Let's dive in!
 12. Save and close the file, then run ``Tools/clinic/clinic.py`` on
     it.  With luck everything worked---your block now has output, and
     a ``.c.h`` file has been generated! Reopen the file in your
-    text editor to see:
-
-    .. code-block:: c
+    text editor to see::
 
        /*[clinic input]
        _pickle.Pickler.dump
@@ -402,9 +410,7 @@ Let's dive in!
 
     For readability, most of the glue code has been generated to a ``.c.h``
     file.  You'll need to include that in your original ``.c`` file,
-    typically right after the clinic module block:
-
-     .. code-block:: c
+    typically right after the clinic module block::
 
        #include "clinic/_pickle.c.h"
 
@@ -1028,7 +1034,9 @@ that value, and an error has been set (``PyErr_Occurred()`` returns a true
 value), then the generated code will propagate the error.  Otherwise it will
 encode the value you return like normal.
 
-Currently Argument Clinic supports only a few return converters::
+Currently Argument Clinic supports only a few return converters:
+
+.. code-block:: none
 
     bool
     int
@@ -1607,7 +1615,9 @@ code probably looks like this::
     #endif /* HAVE_FUNCTIONNAME */
 
 And then in the ``PyMethodDef`` structure at the bottom the existing code
-will have::
+will have:
+
+.. code-block:: none
 
     #ifdef HAVE_FUNCTIONNAME
     {'functionname', ... },
@@ -1657,7 +1667,9 @@ extra code when using the "block" output preset?  It can't go in the output bloc
 because that could be deactivated by the ``#ifdef``.  (That's the whole point!)
 
 In this situation, Argument Clinic writes the extra code to the "buffer" destination.
-This may mean that you get a complaint from Argument Clinic::
+This may mean that you get a complaint from Argument Clinic:
+
+.. code-block:: none
 
     Warning in file "Modules/posixmodule.c" on line 12357:
     Destination buffer 'buffer' not empty at end of file, emptying.
@@ -1677,7 +1689,9 @@ wouldn't make any sense to the Python interpreter.  But using Argument Clinic
 to run Python blocks lets you use Python as a Python preprocessor!
 
 Since Python comments are different from C comments, Argument Clinic
-blocks embedded in Python files look slightly different.  They look like this::
+blocks embedded in Python files look slightly different.  They look like this:
+
+.. code-block:: python3
 
     #/*[python input]
     #print("def foo(): pass")