fix appveyor/nuget

UPnP/nuget_pack.ps1

@@ -0,0 +1,19 @@
+$project = "UPnP"
+$root = (split-path -parent $MyInvocation.MyCommand.Definition) + '\..'
+#$version = [System.Reflection.Assembly]::LoadFile("$root\$project\bin\Debug\$project.dll").GetName().Version
+
+$versionStr = "{0}" -f ($env:APPVEYOR_REPO_TAG_NAME)
+
+if (-not ([string]::IsNullOrEmpty($versionStr))) {
+  Write-Host "Setting $project .nuspec version tag to $versionStr"
+
+  $content = (Get-Content $root\$project\$project.nuspec) 
+  $content = $content -replace '\$version\$',$versionStr
+
+  $content | Out-File $root\$project\$project.compiled.nuspec
+
+  & nuget pack $root\$project\$project.compiled.nuspec
+}
+else {
+  Write-Host "Version string is empty, possibly dry run or APPVEYOR_REPO_TAG_NAME environment variable is not set"
+}