Updates to @actions/artifact (#396)

* Add support for 429s and Exponential backoff

* Refactor status-reporter so it can be used with download and upload

* Extra logs

* Fixes around download & gzip

* Cleanup headers and add extra tests

* Improved Docs

* Spelling bloopers

* Improved error messages

* User http client version 1.0.7

docs/implementation-details.md

@@ -6,9 +6,13 @@ Warning: Implementation details may change at any time without notice. This is m
 
 ![image](https://user-images.githubusercontent.com/16109154/77190819-38685d80-6ada-11ea-8281-4703ff8cc025.png)
 
+## Retry Logic when downloading an individual file
+
+![image](https://user-images.githubusercontent.com/16109154/78555461-5be71400-780d-11ea-9abd-b05b77a95a3f.png)
+
 ## Proxy support
 
-This package uses the `@actions/http-client` NPM package internally which supports proxied requests out of the box. 
+This package uses the `@actions/http-client` NPM package internally which supports proxied requests out of the box.
 
 ## HttpManager