[STYLE] add isort and autopep8 config files and check on CI (#423)

Also a fix a few more style issues from the "aggressive" mode of autopep8.

python/triton/code_gen.py

@@ -852,7 +852,7 @@ class Autotuner:
         else:
             config = self.configs[0]
         self.best_config = config
-        if config.pre_hook != None:
+        if config.pre_hook is not None:
             config.pre_hook(self.nargs)
         return self.kernel(*args, num_warps=config.num_warps, num_stages=config.num_stages, **kwargs, **config.kwargs)