Add useToJSON option

[fregante]

Closes #66

[sindresorhus]

Suggested change

	Indicate whether to use a `toJSON` method if encountered in the object.
	Indicate whether to use a `.toJSON()` method if encountered in the object.

[sindresorhus]

I think this should explain in prose when you would want to turn it off.

[fregante]

Done. Also added a link to MDN in the readme https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#tojson_behavior

[sindresorhus]

This does not feel like a realistic example. No one would be doing this.

[sindresorhus]

Do we really need an example? Just explain the scenarios of when it would be useful.

[fregante]

I dropped the example from the readme too. I suppose this could work in case you change your mind:

```js
import {serializeError} from 'serialize-error';

class CustomError extends Error {
	name = 'CustomError';
	constructor(message) {
		this.time = new Date()
	}
	toJSON() {
		return {
			name: 'CustomError'
		};
	}
}

const error = new CustomError('🦄');

console.log(serializeError(error));
//=> {name: 'CustomError'}

console.log(serializeError(error, {useToJSON: false}));
//=> {name: 'CustomError', message: '🦄', time: '1970-01-01T00:00:00.000Z' stack: 'etc'}
```

[sindresorhus]

Suggested change

	}
	}

[sindresorhus]

Too cramped :P

[fregante]

I just copy-pasted your code 😎

[sindresorhus]

Not mine: 34655eb#diff-13876b4beb64b9f156474dc78f9c923952a7ca210d4507b6b3135bbe244f8a60R219-R239

[fregante]

Who reviewed and merged #38? 😜

[sindresorhus]

Can you fix the merge conflict?