Py2/py3 script that can download macOS components direct from Apple

Can also now build Internet Recovery USB installers from Windows using [dd](http://www.chrysocome.net/dd) and [7zip](https://www.7-zip.org/download.html).

Thanks to:

* FoxletFox for [FetchMacOS](http://www.insanelymac.com/forum/topic/326366-fetchmacos-a-tool-to-download-macos-on-non-mac-platforms/) and outlining the URL setup
* munki for his [macadmin-scripts](https://github.com/munki/macadmin-scripts)
* timsutton for [brigadier](https://github.com/timsutton/brigadier)