Improve the unity build process.

.gitmodules

@@ -2,3 +2,7 @@
 	path = BuildUtils
 	url = https://github.com/aaubry/BuildUtils.git
 	branch = master
+[submodule "BuildUtils.UnityPrerequisites"]
+	path = BuildUtils.UnityPrerequisites
+	url = https://github.com/aaubry/BuildUtils.UnityPrerequisites.git
+	branch = master

build.ps1

@@ -2,52 +2,14 @@
 
 $build_unity = $true
 
-function Download-File($url, $path, $description) {
-  $wc = New-Object System.Net.WebClient
-
-  Write-Host "Downloading $description"
-  Write-Host ": |---------|---------|---------|---------|---------|---------|---------|---------|---------|---------|"
-  Write-Host ": " -NoNewline
-
-  $previousPercentage = 0
-  $e = Register-ObjectEvent -InputObject $wc -EventName DownloadProgressChanged -Action {
-    $currentPercentage = $Args[1].ProgressPercentage
-    for(; $previousPercentage -le $currentPercentage; $previousPercentage++) {
-      Write-Host "#" -NoNewline
-    }
-  }
-  $e = Register-ObjectEvent -InputObject $wc -EventName DownloadFileCompleted -Action {
-    Write-Host " Done"
-    New-Event "DownloadComplete"
-  }
-
-  $canceling = $true
-  $wc.DownloadFileAsync($url, $path, $description)
-  try {
-    $e = Wait-Event "DownloadComplete"
-    $canceling = $false
-  }
-  finally {
-    if($canceling) {
-      Write-Host " - cancelling - " -NoNewline
-    }
-    $wc.CancelAsync()
-    $e = Wait-Event "DownloadComplete"
-    Remove-Event "DownloadComplete"
-    Write-Host ""
-  }
-}
-
 $targets = "Release-Unsigned", "Release-Signed", "Release-Portable-Unsigned", "Release-Portable-Signed"
 
 if($build_unity) {
   $targets += "Release-UnitySubset-v35"
 
-  Download-File "https://visualstudiogallery.msdn.microsoft.com/20b80b8c-659b-45ef-96c1-437828fe7cf2/file/92287/8/Visual%20Studio%202013%20Tools%20for%20Unity.msi" "$env:TEMP\Unity.msi" "VS Tools for Unity"
-
-  Write-Host "Installing VS Tools for Unity... " -NoNewline
-  & .\BuildUtils\MsiInstaller\bin\Release\MsiInstaller.exe "$env:TEMP\Unity.msi"
-  Write-Host "Done"
+  cd BuildUtils.UnityPrerequisites
+  .\install.ps1
+  cd ..
 }
 
 $targets |