Add xamarin build batch files.

Author: yfakariya

PackAll.bat

@@ -0,0 +1,6 @@
+@echo off
+call PackXamarin.bat
+pause
+call Pack.bat
+pause
+:: Rename .latest manually and upload it with .nuget\nuget.exe

PackXamarin.bat

@@ -0,0 +1 @@
+@powershell .\packxamarin.ps1 %1

PackXamarin.ps1

@@ -0,0 +1,18 @@
+param([Switch]$Rebuild)
+
+[string]$temp = '.\nugettmp'
+[string]$builder = "$env:windir\Microsoft.NET\Framework\v4.0.30319\MSBuild.exe"
+
+[string]$sln = 'MsgPack.Xamarin.sln'
+
+[string]$nuspec = 'MsgPack.nuspec'
+
+$buildOptions = @()
+if( $Rebuild )
+{
+    $buildOptions += '/t:Rebuild'
+}
+
+$buildOptions += '/p:Configuration=Release'
+# build
+&$builder $sln $buildOptions