feat: add .getAll() to get all config items

[wy-luke]

Assuming that I have a config like below:

{
  "a": "a",
  "b": "b",
  "c": "c",
  "d": "d"
}

To get all configs, I must use get(xx) four times. I think maybe it's a good idea to use get() to retrieve all configs at one time.
When using electron, it can also get all configs with only one disk IO.

[sindresorhus]

This should be a separate method.

[wy-luke]

@sindresorhus How about this: 7019c7c

[sindresorhus]

Needs a test.

[wy-luke]

@sindresorhus All done. Take a look plz.

[sindresorhus]

I just realized, this already exists as config.store.

[wy-luke]

I just realized, this already exists as config.store.

I think getAll would be more clear and easy to know. Besides, getAll can return {} when config.store is null or undefined, right?

But still, it's up to you. ❤️

[sindresorhus]

Besides, getAll can return {} when config.store is null or undefined, right?

No, it always returns an object.

[sindresorhus]

I think .store is good enough.

[wy-luke]

@sindresorhus At least, adding this usage to the Readme is necessary. It's easy to use but too hard to know it, even you realize its existence later. 😂