Declare Python 3.11 support in package metadata

Author: webknjaz

setup.cfg

@@ -25,6 +25,7 @@ classifiers =
   Programming Language :: Python :: 3.8
   Programming Language :: Python :: 3.9
   Programming Language :: Python :: 3.10
+  Programming Language :: Python :: 3.11
   Development Status :: 5 - Production/Stable
   Operating System :: POSIX
   Operating System :: MacOS :: MacOS X