.NET Core 2+ Naming and Versioning

New file name structure for the runtime and the CLI
per: https://github.com/dotnet/designs/issues/2

The renaming of assets, therefore the dotnet installation scripts must change to accommodate.

Trivial:
"Write-Host" should be "Write-Output"

scripts/use-dev.ps1

@@ -12,5 +12,5 @@ if (Test-Path $stage2) {
         $env:PATH="$stage2;$env:PATH"
     }
 } else {
-    Write-Host "You don't have a dev build in the 'artifacts\win10-x64\stage2' folder!"
+    Write-Output "You don't have a dev build in the 'artifacts\win10-x64\stage2' folder!"
 }