private void addError(String error) {
        if (errors.size() < MAX_ERRORS) {
            errors.add(error);
        } else if (errors.size() == MAX_ERRORS) {
            errors.add("Reached maximum limit of errors (" + MAX_ERRORS + "). Not collecting any more.");
        }
    }
Base class for unpacking document operation streams and pushing to feed
access points.

@author Thomas Gundersen
@author steinar
vespaclient-core/src/main/java/com/yahoo/feedapi/Feeder.java