UnitsNet.Net35: Add pre-build step to regenerate code

Ideally this was a solution-wide pre-build step, but only way to achieve
that is to add a new project and let the others depend on it, but seems
a bit overkill. If you edit the source code (shared among the core
projects), then the Net35 project will rebuild when you build the
solution.

Author: angularsen

UnitsNet/UnitsNet.Net35.csproj

@@ -48,6 +48,9 @@
     <Service Include="{508349B6-6B84-4DF5-91F0-309BEEBAD82D}" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <PropertyGroup>
+    <PreBuildEvent>call $(ProjectDir)..\GenerateUnits.bat</PreBuildEvent>
+  </PropertyGroup>
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it.
        Other similar extension points exist, see Microsoft.Common.targets.
   <Target Name="BeforeBuild">