Download API (#858)

* Create APIReview_CustomDownload (#751)

* Create APIReview_CustomDownload

* changed to md

* small changes

* Adding API details

* add deferral, .net, and format

* use deferral and update names

* formatting code

* use new names in .net

* use new namse in .net

* use deferral in .net

* update comments

* self contained .net example

Co-authored-by: Viktoria Zlatinova <vizlatin@microsoft.com>

* Rename APIReview_CustomDownload.md to CustomDownload.md

* Add DownloadItem

* updated intro

* Add progress events

* updated intro

* update terminology

* fixing enums and sample code

* expected download size in bytes

* use DateTime object

* Add paused interrupt reason

* update description

* clarify resume()

* update description and change uint to int

* Update specs/CustomDownload.md

Co-authored-by: David Risney <dave@deletethis.net>

* Update specs/CustomDownload.md

Co-authored-by: David Risney <dave@deletethis.net>

* Apply suggestions from code review

Co-authored-by: David Risney <dave@deletethis.net>

* add comments to .net sample code

* change uint to int

* improve .net sample code comment

* reentrancy comment

* remove part of description

Co-authored-by: Jason Stephen <22718545+jasonstephen15@users.noreply.github.com>
Co-authored-by: Viktoria Zlatinova <vizlatin@microsoft.com>
Co-authored-by: David Risney <dave@deletethis.net>

Author: 3 people