Add hooks for new pycodestyle checks.

Add hooks for new checks introduced in pycodestyle 2.4.0.
For details of the changes to pycodestyle, see:
https://pycodestyle.readthedocs.io/en/latest/developer.html

setup.py

@@ -119,6 +119,8 @@ setuptools.setup(
             PEP8_PLUGIN('python_3000_raise_comma'),
             PEP8_PLUGIN('python_3000_not_equal'),
             PEP8_PLUGIN('python_3000_backticks'),
+            PEP8_PLUGIN('python_3000_invalid_escape_sequence'),
+            PEP8_PLUGIN('python_3000_async_await_keywords'),
         ],
         'flake8.report': [
             'default = flake8.formatting.default:Default',