code: func (st StackTrace) formatSlice(s fmt.State, verb rune) {
  	io.WriteString(s, "[")
  	for i, f := range st {
  		if i > 0 {
  			io.WriteString(s, " ")
  		}
  		f.Format(s, verb)
  	}
  	io.WriteString(s, "]")
  }
docs: // formatSlice will format this StackTrace into the given buffer as a slice of
  // Frame, only valid when called with '%s' or '%v'.