* Convert stat_result to proper dictionary so that field names are
  retained after serialization

* Add ability to ignore directories through command line arguments,
  explicitly add "ignored" field on ignored directories

It was decided that JSON was not a suitable format because bytes
serialization support is lacking. MsgPack supports it and is more
efficient, also it is the internal serialization format for Fluentd
which we will most probably use for ingesting data in a central
place.