Reports the minimum or maximum daily feed value

Adds the option to record the minimum or maximum daily feed value, which resets to current feed value at midnight.
For example, the maximum or Minimum daily temperature.
The reset allows the function to operate with sub zero data (the mysql default is null which would otherwise create problems).
The feed is only updated whenever a 'new max' or 'new min' is encountered.
Thanks to Jerome for his help developing this.

Paul