Support `Output` Element

[icnocop]

Hi.

Thank you for IsolatedTask.

I'd like to request support for the Output Element.

For example,

    <IsolatedTask AssemblyFile="$(__SpecFlowTasksFullPath)"
                  TaskNameWithNamespace="TechTalk.SpecFlow.Tools.MsBuild.GenerateAll"
                  ParameterNames="ShowTrace;BuildServerMode;OverwriteReadOnlyFiles;ProjectPath;ForceGeneration;VerboseOutput"
                  ParameterValues="$(ShowTrace);$(BuildServerMode);$(OverwriteReadOnlyFiles);$(MSBuildProjectFullPath);$(ForceGeneration);$(VerboseOutput)">
      <Output TaskParameter="GeneratedFiles" ItemName="SpecFlowGeneratedFiles" />
    </IsolatedTask>

Currently, the following error occurs:

error MSB4131: The "GeneratedFiles" parameter is not supported by the "IsolatedTask" task. Verify the parameter exists on the task, and it is a gettable public instance property.

Thank you.