public Builder setHandler(Handler handler) {
      this.handler = handler;
      return this;
    }
<p>Set a custom handler that will be used to post all callbacks to</p>

<p>See {@link Shell.Interactive} for further details on threading and handlers</p>

@param handler
    Handler to use
@return This Builder object for method chaining
imitate/src/main/java/com/engineer/imitate/shell/Shell.java