Make deciding serialization happens on I/O thread or biz thread easier.

[chickenlj]

decode.in.io

• default value is true, which means decode happens on I/O thread.
• the way to change the value is not direct enough, at least there should have a document tell us how to do it.

 <dubbo:application name="demo-consumer">
       <dubbo:parameter key="decode.in.io" value="false"/>
   </dubbo:application>

[cvictory]

I have add a article on http://dubbo.apache.org/