[STYLE] check python with flake8 (#424)

I've been using this locally to find errors without running tests, and now that we're using autopep8, it passes with minimal suppressions. This is also what turned up the issues with the tutorials, which were fixed in #422.

python/tutorials/01-vector-add.py

@@ -65,7 +65,7 @@ def add(x: torch.Tensor, y: torch.Tensor):
     #  - each torch.tensor object is implicitly converted into a pointer to its first element.
     #  - `triton.jit`'ed functions can be index with a launch grid to obtain a callable GPU kernel
     #  - don't forget to pass meta-parameters as keywords arguments
-    pgm = add_kernel[grid](x, y, output, n_elements, BLOCK_SIZE=1024)
+    add_kernel[grid](x, y, output, n_elements, BLOCK_SIZE=1024)
     # We return a handle to z but, since `torch.cuda.synchronize()` hasn't been called, the kernel is still
     # running asynchronously at this point.
     return output