title: Simpler use of TypeAdapterFactory
body: <p>AFAIK the most flexible gson customization is possible via <code>TypeAdapterFactory</code>, however it may get needlessly complicated. It forces me to write for each handled class both <code>read</code> and <code>write</code>, while sometimes only one method is really needed. Moreover, sometimes a <code>JsonSerializer</code> and/or <code>JsonDeserializer</code> were much easier to write, e.g. <a href="https://stackoverflow.com/a/7773201/581205">like here</a>. This leads me to these questions:</p>
  
  <ul>
  <li>Is it possible to write a <code>TypeAdapter</code> which simply delegates one of its methods (e.g. writing of <code>ImmutableList</code> to writing of <code>List</code>)?</li>
  <li>Is it possible to somehow use <code>JsonSerializer</code> and/or <code>JsonDeserializer</code> together with the <code>TypeAdapterFactory</code>? Alternatively, is there a factory for them?</li>
  </ul>