code: <E> Observable<E> addLogging(@NonNull Observable<E> obs, @NonNull Logger log, final String msg) {
          return obs.doOnNext(r -> log(log, (ComapiResult) r, msg))
                  .doOnError(t -> log(log, t, msg));
      }
docs: Add logging to observable.
  
  @param obs Observable to add logging for.
  @param log Logger instance.
  @param msg Message with which the log should start with.
  @param <E> Class of the service call result.
  @return Observable for API call.