Add `inplace` input param to `add_prefix` and `add_suffix`
I find myself often wanting to rename columns with a prefix or suffix **inplace** and want to avoid creating copies, so I end up with code as:

`df.rename(columns={col: add_prefix_or_suffix_func_prototype(col) for col in df.columns}, inplace=True)`

It would be a simple feature addition if the `add_prefix` and `add_suffix` would expose this `kwarg` (**inplace**) to simplify the code to:

`df.add_prefix('prefix', **inplace**=True)  # same for add_suffix`