Added missing Nuspec file

Added missing Nuspec file

Build/MQTTnet.nuspec

@@ -0,0 +1,44 @@
+<?xml version="1.0"?>
+<package >
+  <metadata>
+    <id>MQTTnet</id>
+    <version>0</version>
+    <authors>Christian Kratky</authors>
+    <owners>Christian Kratky</owners>
+    <licenseUrl>https://github.com/chkr1011/MQTTnet/blob/master/LICENSE</licenseUrl>
+    <projectUrl>https://github.com/chkr1011/MQTTnet</projectUrl>
+    <iconUrl>https://raw.githubusercontent.com/chkr1011/MQTTnet/master/Images/Logo_128x128.png</iconUrl>
+    <requireLicenseAcceptance>false</requireLicenseAcceptance>
+    <description>MQTTnet is a .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker).</description>
+    <releaseNotes>* [.NET Standard] Added support for .NET Standard 1.3 (Thanks to 1iveowl)</releaseNotes>
+    <copyright>Copyright Christian Kratky 2016-2017</copyright>
+    <tags>MQTT MQTTClient MQTTServer MQTTBroker Broker</tags> 
+    <dependencies>
+
+      <group targetFramework="netstandard1.3">
+        <dependency id="NETStandard.Library" version="1.6.1" />
+        <dependency id="System.Net.Security" version="4.3.1" />
+      </group>
+      
+      <group targetFramework="uap10.0">
+        <dependency id="Microsoft.NETCore.UniversalWindowsPlatform" version="5.3.3" />
+      </group>
+
+    </dependencies>
+  </metadata>
+
+  <files>
+    <!-- .NET Standard 1.3 -->
+    <file src="..\Frameworks\MQTTnet.Netstandard\bin\Release\netstandard1.3\MQTTnet.Core.*" target="lib\netstandard1.3\"/>
+    <file src="..\Frameworks\MQTTnet.Netstandard\bin\Release\netstandard1.3\MQTTnet.*" target="lib\netstandard1.3\"/>
+
+    <!-- Universal Windows -->
+    <file src="..\Frameworks\MQTTnet.UniversalWindows\bin\Release\MQTTnet.Core.*" target="lib\uap10.0\"/>
+    <file src="..\Frameworks\MQTTnet.UniversalWindows\bin\Release\MQTTnet.*" target="lib\uap10.0\"/>
+
+    <!-- .NET Framework -->
+    <file src="..\Frameworks\MQTTnet.NetFramework\bin\Release\MQTTnet.Core.*" target="lib\net45\"/>
+    <file src="..\Frameworks\MQTTnet.NetFramework\bin\Release\MQTTnet.*" target="lib\net45\"/>
+    
+  </files>
+</package>