Add support for KeysReaderRecord.getListVal

[rrelledge]

The generated Javadoc for GearsBuilder.flatMap() has an example that uses getListVal():

GearsBuilder.CreateGearsBuilder(reader).
  	flatMap(r->{
  		return r.getListVal();
  	}); 

However, KeysReaderRecord.getListVal() has a comment that says: "Currently not supported and returns null".

When I tried out the flatMap example, I got this output:

1) (empty array)
2) 1) "Got null record on flat mapper"