bpo-20260: Implement non-bitwise unsigned int converters for Argument Clinic. (python/cpython#8434)

GitHub-Issue-Link: python/cpython#64459

Author: serhiy-storchaka

Doc/howto/clinic.rst

@@ -878,6 +878,12 @@ converter::
     Write a pickled representation of obj to the open file.
     [clinic start generated code]*/
 
+One advantage of real converters is that they're more flexible than legacy
+converters.  For example, the ``unsigned_int`` converter (and all the
+``unsigned_`` converters) can be specified without ``bitwise=True``.  Their
+default behavior performs range checking on the value, and they won't accept
+negative numbers.  You just can't do that with a legacy converter!
+
 Argument Clinic will show you all the converters it has
 available.  For each converter it'll show you all the parameters
 it accepts, along with the default value for each parameter.