Log a warning when the [wheel] section is used (#239)

Has been considered legacy since
b2d2165 (2014-03-17) or version 0.23.0.
However, projects continue to use the [wheel] section. Adding a warning
might help move more projects to the recommended [bdist_wheel].

wheel/bdist_wheel.py

@@ -125,6 +125,7 @@ def finalize_options(self):
         wheel = self.distribution.get_option_dict('wheel')
         if 'universal' in wheel:
             # please don't define this in your global configs
+            logger.warn('The [wheel] section is deprecated. Use [bdist_wheel] instead.')
             val = wheel['universal'][1].strip()
             if val.lower() in ('1', 'true', 'yes'):
                 self.universal = True