message: Improve documentation of inbound_path
diff: @@ -80,13 +80,19 @@ public:
  /// Stores statistics for measuring complexity of incoming batches.
  struct stats_t {
  + /// Wraps a time measurement for a single processed batch.
  struct measurement {
  + /// Number of items in the batch.
  long batch_size;
  + /// Elapsed time for processing all elements of the batch.
  timespan calculation_time;
  };
  + /// Wraps the resulf of `stats_t::calculate()`.
  struct calculation_result {
  + /// Number of items per credit cycle.
  long max_throughput;
  + /// Number of items per batch to reach the desired batch commplexity.
  long items_per_batch;
  };
  