Make plt.style.use accept path-like objects in addition to string

`plt.style.use(style)` accepts a `str`, `dict`, or `list`. The `str `can be either the name of a style or a path/URL to a style file. I propose that this also accept a pathlike object (`pathlib.Path`) so that it is unneccesary to cast it like `plt.style.use(str(my_path))`, but accept it like this `plt.style.use(my_path)`.

There may be other places in the code that accepts file paths as strings.