add build.ps1 to align with PSES and other PowerShell projects (#1199)

* add build.ps1

* travis feedback

* address steve's feedback

Author: TylerLeonhardt

build.ps1

@@ -0,0 +1,115 @@
+#!/usr/bin/env pwsh
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License.
+
+param(
+    [Parameter(ParameterSetName="Bootstrap")]
+    [switch]
+    $Bootstrap,
+
+    [Parameter(ParameterSetName="Build")]
+    [switch]
+    $Clean,
+
+    [Parameter(ParameterSetName="Build")]
+    [switch]
+    $Test
+)
+
+$NeededTools = @{
+    VSCode = "Visual Studio Code"
+    NodeJS = "Node.js 6.0 or higher"
+    PowerShellGet = "PowerShellGet latest"
+    InvokeBuild = "InvokeBuild latest"
+}
+
+function needsVSCode () {
+    try {
+            $vscodeVersion = (code -v)
+            if (-not $vscodeVersion) {
+                Throw
+            }
+    } catch {
+        try {
+            $vscodeInsidersVersion = (code-insiders -v)
+            if (-not $vscodeInsidersVersion) {
+                Throw
+            }
+        } catch {
+            return $true
+        }
+    }
+    return $false
+}
+
+function needsNodeJS () {
+    try {
+        $nodeJSVersion = (node -v)
+
+    } catch {
+        return $true
+    }
+    return ($nodeJSVersion.Substring(1,1) -lt 6)
+}
+
+function needsPowerShellGet () {
+    if (Get-Module -ListAvailable -Name PowerShellGet) {
+        return $false
+    }
+    return $true
+}
+
+function needsInvokeBuild () {
+    if (Get-Module -ListAvailable -Name InvokeBuild) {
+        return $false
+    }
+    return $true
+}
+
+function getMissingTools () {
+    $missingTools = @()
+
+    if (needsVSCode) {
+        $missingTools += $NeededTools.VSCode
+    }
+    if (needsNodeJS) {
+        $missingTools += $NeededTools.NodeJS
+    }
+    if (needsPowerShellGet) {
+        $missingTools += $NeededTools.PowerShellGet
+    }
+    if (needsInvokeBuild) {
+        $missingTools += $NeededTools.InvokeBuild
+    }
+
+    return $missingTools
+}
+
+function hasMissingTools () {
+    return ((getMissingTools).Count -gt 0)
+}
+
+if ($Bootstrap) {
+    $string = "Here is what your environment is missing:`n"
+    $missingTools = getMissingTools
+    if (($missingTools).Count -eq 0) {
+        $string += "* nothing!`n`n Run this script without a flag to build or a -Clean to clean."
+    } else {
+        $missingTools | ForEach-Object {$string += "* $_`n"}
+        $string += "`nAll instructions for installing these tools can be found on VSCode PowerShell's Github:`n" `
+            + "https://github.com/PowerShell/vscode-powershell/blob/master/docs/development.md"
+    }
+    Write-Host "`n$string`n"
+} elseif(hasMissingTools) {
+    Write-Host "You are missing needed tools. Run './build.ps1 -Bootstrap' to see what they are."
+} else {
+    if($Clean) {
+        Invoke-Build Clean
+    }
+
+    Invoke-Build Build
+
+    if($Test) {
+        Invoke-Build Test
+    }
+}