Rustup: Command-line-friendly way to rustup on windows

[vors]

Projects that are building on windows in CI need a one-liner to install and run the rustup.
The same way it works on unix and mac.
Example of a script that people use at the moment in CI https://github.com/rust-onig/rust-onig/blob/68393b487c679c789ee8a762e77f568e75a3128a/appveyor_rust_install.ps1

This script is not a very good because it uses appveyor-specific calls.
A better one may look something like

$client = new-object System.Net.WebClient
$client.DownloadFile('https://win.rustup.rs', "$pwd\rustup-init.exe")
.\rustup-init.exe

This is a powershell script, powershell ships inbox on all windows machines.
Bells and whisles to pass channels and other parameters could be added.

By hosting it on the ps1.rustup.rs, there would be a simple copy-pastable one-liner, like in choco https://chocolatey.org/install

It can be then put on https://rustup.rs/ under windows tab.

[vors]

Related #912

[Diggsey]

Seems like a good idea, although would only really be an improvement for automated systems, so the executable should still be the primary install method.

It might make more sense to save to a temporary directory, or the downloads directory instead of the current directory, and to include -y and the toolchain selector.

@rust-lang-nursery/rustup-rs-owners thoughts?

[vors]

Not only for automated systems.
Here I'm running windows containers on mac, and all I have is a command line. So the "download this installer" is pretty cumbersome way to go. This is just how I'm able to build on both mac and windows locally and rsync things.

[workingjubilee]

@rustbot label: +O-windows