func Opf(format string, a ...interface{}) Op {
	return Op(fmt.Sprintf(format, a...))
}
Opf returns a formatted Op.
package errors
import (
	"errors"
	"fmt"
	"runtime/debug"
	"strings"
)
var Separator = ":\n\t"
type Error struct {
	Op   Op
	Kind Kind
	Err  error
	stack  []byte
	bottom bool
}
type Op string