Added activate.ps1 to set DOTNET_ROOT to Path (#311)

activate.ps1

@@ -0,0 +1,57 @@
+#
+# This file must be used by invoking ". .\activate.ps1" from the command line.
+# You cannot run it directly.
+# To exit from the environment this creates, execute the 'deactivate' function.
+#
+
+function deactivate ([switch]$init) {
+
+    # reset old environment variables
+    if (Test-Path variable:_OLD_PATH) {
+        $env:PATH = $_OLD_PATH
+        Remove-Item variable:_OLD_PATH
+    }
+
+    if (test-path function:_old_prompt) {
+        Set-Item Function:prompt -Value $function:_old_prompt -ea ignore
+        remove-item function:_old_prompt
+    }
+
+    Remove-Item env:DOTNET_ROOT -ea ignore
+    Remove-Item env:DOTNET_MULTILEVEL_LOOKUP -ea ignore
+    if (-not $init) {
+        # Remove the deactivate function
+        Remove-Item function:deactivate
+    }
+}
+
+# Cleanup the environment
+deactivate -init
+
+$_OLD_PATH = $env:PATH
+# Tell dotnet where to find itself
+$env:DOTNET_ROOT = "$PSScriptRoot\.dotnet"
+# Tell dotnet not to look beyond the DOTNET_ROOT folder for more dotnet things
+$env:DOTNET_MULTILEVEL_LOOKUP = 0
+# Put dotnet first on PATH
+$env:PATH = "${env:DOTNET_ROOT};${env:PATH}"
+
+# Set the shell prompt
+if (-not $env:DISABLE_CUSTOM_PROMPT) {
+    $function:_old_prompt = $function:prompt
+    function dotnet_prompt {
+        # Add a prefix to the current prompt, but don't discard it.
+        write-host "($( split-path $PSScriptRoot -leaf )) " -nonewline
+        & $function:_old_prompt
+    }
+
+    Set-Item Function:prompt -Value $function:dotnet_prompt -ea ignore
+}
+
+Write-Host -f Magenta "Enabled the .NET Core environment. Execute 'deactivate' to exit."
+if (-not (Test-Path "${env:DOTNET_ROOT}\dotnet.exe")) {
+    Write-Host -f Yellow ".NET Core has not been installed yet. Run $PSScriptRoot\restore.cmd to install it."
+}
+else {
+    Write-Host "dotnet = ${env:DOTNET_ROOT}\dotnet.exe"
+}