func NewPool(pbs ...*ProgressBar) (pool *Pool) {
	pool = new(Pool)
	pool.Add(pbs...)
	return
}
NewPool initialises a pool with progress bars, but
doesn't start it. You need to call Start manually
package pb
import (
	"io"
	"sync"
	"time"
)
func StartPool(pbs ...*ProgressBar) (pool *Pool, err error) {
	pool = new(Pool)
	if err = pool.Start(); err != nil {
		return
	}
	pool.Add(pbs...)
	return
}