Added missing PS script

Added install-dotnet.ps1 script.

Author: dustinmoris

install-dotnet.ps1

@@ -0,0 +1,88 @@
+# ----------------------------------------------------------
+# Install script to check and download the correct .NET SDK
+# ----------------------------------------------------------
+
+function Test-IsWindows
+{
+    [environment]::OSVersion.Platform -ne "Unix"
+}
+
+function Invoke-Cmd ($cmd)
+{
+    Write-Host $cmd -ForegroundColor DarkCyan
+    if (Test-IsWindows) { $cmd = "cmd.exe /C $cmd" }
+    Invoke-Expression -Command $cmd
+    if ($LastExitCode -ne 0) { Write-Error "An error occured when executing '$cmd'."; return }
+}
+
+function dotnet-version { Invoke-Cmd "dotnet --version" }
+
+function Get-DesiredSdk
+{
+    Get-Content "global.json" | ConvertFrom-Json | % { $_.sdk.version.ToString() }
+}
+
+function Get-NetCoreSdk ($version)
+{
+    $os = if (Test-IsWindows) { "windows" } else { "linux" }
+
+    $response = Invoke-WebRequest `
+                    -Uri "https://www.microsoft.com/net/download/thank-you/dotnet-sdk-$version-$os-x64-binaries" `
+                    -Method Get `
+                    -MaximumRedirection 0 `
+
+    $downloadLink =
+        $response.Links `
+            | Where-Object { $_.onclick -eq "recordManualDownload()" } `
+            | Select-Object -Expand href
+
+    $tempFile  = [System.IO.Path]::GetTempFileName()
+    $webClient = New-Object System.Net.WebClient
+    $webClient.DownloadFile($downloadLink, $tempFile)
+    return $tempFile
+}
+
+function Install-NetCoreSdk ($sdkZipPath)
+{
+    $env:DOTNET_INSTALL_DIR = "$pwd\.dotnetsdk"
+    New-Item $env:DOTNET_INSTALL_DIR -ItemType Directory -Force
+
+    Add-Type -AssemblyName System.IO.Compression.FileSystem;
+    [System.IO.Compression.ZipFile]::ExtractToDirectory($sdkZipPath, $env:DOTNET_INSTALL_DIR)
+    $env:Path = "$env:DOTNET_INSTALL_DIR;$env:Path"
+}
+
+# ----------------------------------------------
+# Install .NET Core SDK
+# ----------------------------------------------
+
+$ErrorActionPreference = "Stop"
+
+# Rename the global.json before making the dotnet --version call
+# This will prevent AppVeyor to fail because it might not find
+# the desired SDK specified in the global.json
+$globalJson = Get-Item "global.json"
+Rename-Item -Path $globalJson.FullName -NewName "global.json.bak" -Force
+
+# Get the current .NET Core SDK version
+$currentSdk = dotnet-version
+
+# After we established the current installed .NET SDK we can put the global.json back
+Rename-Item -Path ($globalJson.FullName + ".bak") -NewName "global.json" -Force
+
+$desiredSdk = Get-DesiredSdk
+
+if ($desiredSdk -eq $currentSdk)
+{
+    Write-Host "The current .NET SDK matches the project's desired .NET SDK: $desiredSDK" -ForegroundColor Green
+    return
+}
+
+Write-Host "The current .NET SDK ($currentSdk) doesn't match the project's desired .NET SDK ($desiredSdk)." -ForegroundColor Yellow
+Write-Host "Attempting to download and install the correct .NET SDK..."
+
+$sdkZipPath = Get-NetCoreSdk $desiredSdk
+Install-NetCoreSdk $sdkZipPath
+
+Write-Host ".NET SDK installation complete." -ForegroundColor Green
+dotnet-version