func (stt StyledText) WithTextf(format string, a ...interface{}) StyledText {
	stt.text = fmt.Sprintf(format, a...)
	return stt
}
WithTextf returns a derived styled text with updated formatted text.
package ui
import (
	"bytes"
	"fmt"
	"strings"
	"github.com/anaseto/gruid"
)
type StyledText struct {
	markups map[rune]gruid.Style
	text    string
	style   gruid.Style
}
func Text(text string) StyledText {
	return StyledText{text: text}
}
func Textf(format string, a ...interface{}) StyledText {
	return StyledText{text: fmt.Sprintf(format, a...)}
}
func NewStyledText(text string, st gruid.Style) StyledText {
	return StyledText{text: text, style: st}
}
func (stt StyledText) Text() string {
	return stt.text
}
func (stt StyledText) WithText(text string) StyledText {
	stt.text = text
	return stt
}