func (e ElementFunc) ProgressElement(state *State, args ...string) string {
	return e(state, args...)
}
ProgressElement just call self func
package pb
import (
	"bytes"
	"fmt"
	"math"
	"strings"
	"sync"
	"time"
)
const (
	adElPlaceholder    = "%_ad_el_%"
	adElPlaceholderLen = len(adElPlaceholder)
)
var (
	defaultBarEls = [5]string{"[", "-", ">", "_", "]"}
)
type Element interface {
	ProgressElement(state *State, args ...string) string
}
type ElementFunc func(state *State, args ...string) string