Docs should include info how to promisify jar

[thamerla]

I would like to use promises but I have no clue how to promisify methods using built-in util.promisify. Docs should support this if it's not currently possible to implement promises on their own.

[stash]

I suspect that util.promisfy should Just Work (tm) but I'll write up some test cases and update README.md to reflect the preferred method.

Since we support minimum node.js v6, and util.promisify was added in v8, tough-cookie unfortunately can't (yet!) switch to supporting this automatically. So, I'd like to explore a wrapper package that offers a promisify-ed API.

[stash]

See also: #66

[thamerla]

@stash I saw that one and it prompted me to write this issue.

[bshevlin]

@stash Bluebird has a good backwards-compatible promisification function and would probably help. They also have util functions that could help with backwards compatibility.

An example from Bluebird's docs that simultaneously supports promises and callbacks:

function getDataFor(input, callback) {
    return dataFromDataBase(input).asCallback(callback);
}

[shivam-tripathi]

This should be useful:

const cookieJar = new tough.CookieJar();
const setCookie = util.promisify(cookieJar.setCookie.bind(cookieJar));
await setCookie('billi=0', 'https://www.catcat.com/', {
    ignoreError: false
});

[awaterma]

We now support promises in the 4.x release. I think this issue is asking for better documentation, and some examples? Or should we close this out?

[colincasey]

this should be addressed in #234

[wjhsf]

#234 has been merged with updates to the README.