Update build script to target multiple frameworks

Author: Cory Thompson

build/package/WebPush.nuspec renamed to WebPush.nuspec

@@ -0,0 +1,20 @@
+rmdir /S /Q "build" 2>nul
+
+mkdir build\package\lib\netcoreapp1.0
+mkdir build\package\lib\netcoreapp1.1
+mkdir build\package\lib\netstandard1.3
+mkdir build\package\lib\net45
+mkdir build\package\lib\net46
+
+copy WebPush.nuspec build\package\
+
+dotnet restore
+dotnet build --configuration=Release WebPush\WebPush.csproj
+
+copy WebPush\bin\Release\netcoreapp1.0\WebPush.dll build\package\lib\netcoreapp1.0\WebPush.dll
+copy WebPush\bin\Release\netcoreapp1.1\WebPush.dll build\package\lib\netcoreapp1.1\WebPush.dll
+copy WebPush\bin\Release\netstandard1.3\WebPush.dll build\package\lib\netstandard1.3\WebPush.dll
+copy WebPush\bin\Release\net45\WebPush.dll build\package\lib\net45\WebPush.dll
+copy WebPush\bin\Release\net46\WebPush.dll build\package\lib\net46\WebPush.dll
+
+nuget pack build\package\WebPush.nuspec