Improve NLog XSD Schema with better support for Layout-options

[snakefoot]

Current NLog Schema complains about Layout-options when not declared like simple attributes:

<?xml version="1.0" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      autoReload="true">
    <targets>
        <target name="database" xsi:type="Database">

            <dbProvider>mssql</dbProvider>

            <commandText>
                insert into LogTable(time_stamp,level,logger,message) values(@time_stamp, @level, @logger, @message);
            </commandText>

            <parameter name="@time_stamp" layout="${date}" />
            <parameter name="@level" layout="${level}" />
            <parameter name="@logger" layout="${logger}" />
            <parameter name="@message" layout="${message}" />
        </target>
    </targets>

    <rules>
        <logger name="*" minlevel="Debug" writeTo="database" />
    </rules>
</nlog>

Could be nice if the NLog XSD Schema would accept the above as valid (Notice <dbProvider> works because xsi:string, but not <commandText>)