XMLHttpRequest polyfill for node.js

Based on https://github.com/pwnall/node-xhr2

* Adds support for cookies
* Adds in-project TypeScript type definitions
* Switched to TypeScript

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* saved in XMLHttpRequest.cookieJar
* saved between redirects
* saved between requests
* can be cleared by doing:
``typescript
import * as Cookie from 'cookiejar';
XMLHttpRequest.cookieJar = Cookie.CookieJar();
`

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* Provide full XMLHttpRequest features to Angular Universal HttpClient &
node-angular-http-client

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#### 1.1.0
* added saving of cookies between requests, not just redirects
* bug fixes
* most tests from xhr2` ported over and passing