Explicit resource management (using keyword)

[pmcelhaney]

https://github.com/tc39/proposal-explicit-resource-management

The ultimate goal is to support the using keyword.

import {temporaryFiles} from "using-temporary-files";

const api = using temporaryFiles();

// api.add(...)
// api.path(...)
// etc. 

It won't take much effort to implement. I just haven't gotten around to it yet.

The existing promise-based API will remain.