code: func (c *Config) GetUint64(key string) (u uint64, err error) {
  	val, ok := (*c)[key]
  	if !ok {
  		return 0, ErrNoSuchKey
  	}
  	switch val.(type) {
  	case uint8:
  		return uint64(val.(uint8)), nil
  	case uint16:
  		return uint64(val.(uint16)), nil
  	case uint32:
  		return uint64(val.(uint32)), nil
  	case uint:
  		return uint64(val.(uint)), nil
  	case uint64:
  		return val.(uint64), nil
  	case float64:
  		// json loads float64 so handle that case
  		return uint64(val.(float64)), nil
  	default:
  		return 0, fmt.Errorf("Wrong type for %s (Type:%T Expecting:%T)", key, val, u)
  	}
  }
docs: // GetUint64 gets the value associated to a key as uint64
  // return (uint64, error)