Add sort_keys option

[cbw512]

As a prettier option and a big improval for tests that compare a toml file, I think a sort_keys like json option is useful.It ensure two toml file with same content will be able to do a text-compare after sorting keys.

[hukkin]

Thanks for the issue!

As the README file mentions, Tomli-W respects sort order of the input dict, so you can do

import tomli_w

def order_dict(d):
    return {k: order_dict(v) if isinstance(v, dict) else v for k, v in sorted(d.items())}

d = {"b": 2, "a": {"b": 2, "a": 1}}
sorted_toml = tomli_w.dumps(order_dict(d))

It's trivial enough to come up with a sort function of your own that I'm not sure Tomli-W needs to ship with one (that may not sort exactly the way you want).