message: add ascii command f for feedback
diff: @@ -155,6 +155,19 @@ void ASCII_protocol_process_line(const uint8_t* buffer, size_t len, StreamSink&
  axes[motor_number]->controller_.move_to_pos(goal_point);
  }
  + } else if (cmd[0] == 'f') { // feedback
  + unsigned motor_number;
  + int numscan = sscanf(cmd, "f %u", &motor_number);
  + if (numscan < 1) {
  + respond(response_channel, use_checksum, "invalid command format");
  + } else if (motor_number >= AXIS_COUNT) {
  + respond(response_channel, use_checksum, "invalid motor %u", motor_number);
  + } else {
  + respond(response_channel, use_checksum, "%f %f",
  + (double)axes[motor_number]->encoder_.pos_estimate_,
  + (double)axes[motor_number]->encoder_.vel_estimate_);
  + }
  +
  } else if (cmd[0] == 'h') { // Help
  respond(response_channel, use_checksum, "Please see documentation for more details");
  respond(response_channel, use_checksum, "");
  