code: func (c *ConfigFile) MustFloat64(section, key string, defaultVal ...float64) float64 {
  	value, err := c.Float64(section, key)
  	if len(defaultVal) > 0 && err != nil {
  		return defaultVal[0]
  	}
  	return value
  }
docs: // MustFloat64 always returns value without error,
  // it returns 0.0 if error occurs.