Recording electorate and spoilt values

[jf1]

Optional 'total electorate' field is useful but turnout %age isn't - the latter and total valid votes cast should be calculated by dc so inputters can use as checksums.

Input for electorate size must be optional as it's often not provided. When it is provided I believe it's the only way of knowing the 2016 value aka it's unique and useful data.

Making 'spoilt' optional would help for times when it's not provided, or just add some text to encourage people to record '-1' perhaps with code to display that as 'unknown' in results tables.

[jf1]

These results also contain postal and per-polling-station electorate and turnout values, so it'd be nice if future systems were able to support this too.