func TagString(key string, val string) Tag {
	return Tag{Key: key, Value: val}
}
TagString new string tag.
package trace
const (
	TagComponent = "component"
	TagDBInstance = "db.instance"
	TagDBStatement = "db.statement"
	TagDBType = "db.type"
	TagDBUser = "db.user"
	TagError = "error"
	TagHTTPMethod = "http.method"
	TagHTTPStatusCode = "http.status_code"
	TagHTTPURL = "http.url"
	TagMessageBusDestination = "message_bus.destination"
	TagPeerAddress = "peer.address"
	TagPeerHostname = "peer.hostname"
	TagPeerIPv4 = "peer.ipv4"
	TagPeerIPv6 = "peer.ipv6"
	TagPeerPort = "peer.port"
	TagPeerService = "peer.service"
	TagSamplingPriority = "sampling.priority"
	TagSpanKind = "span.kind"
	TagAnnotation = "legacy.annotation"
	TagAddress    = "legacy.address"
	TagComment    = "legacy.comment"
)
const (
	LogErrorKind = "error.kind"
	LogErrorObject = "error.object"
	LogEvent = "event"
	LogMessage = "message"
	LogStack = "stack"
)
type Tag struct {
	Key   string
	Value interface{}
}