function report( id, severity, message, node ) {
	var start = null;
	var end = null;
	if ( node ) {
		start = node.start;
		end = node.end;
	}
	this.messages.push({
		'id': id,
		'severity': severity,
		'message': message,
		'start': start,
		'end': end
	});
}
Registers violation of lint rule.

@private
@param {string} id - rule id
@param {string} severity - rule severity (`error` or `warn`)
@param {string} message - error message
@param {Object} node - node for which to log error