counter: 1.4.0 - Refined output JSON to match the new general stats-format

counter: 1.4.0 - Refined output JSON to match the new general stats-format

* Changed the type-mapping for `Word` from `word` to `key`.
* Refined the class `Word`, that defines the JSON for the output key.
** Added attribute `type` with fixed value `POPULAR`.
** Renamed attribute `user` to `channel`.
** Renamed attribute `word` to `key`.
* Refined the class `WordCounter`, that defines the JSON for the output
  value.
** Renamed attribute `word` to `key`.
* Adapted test-classes and -cases accordingly.