Add SecondsSinceMidnight; perhaps even allow others to define custom fields

[fourpastmidnight]

I would like to see a SecondsSinceMidnight field so that I can represent the build timestamp in a compact format: {yy}{doy}.{ssm}, which is 2-digit year followed by the day of the year and the seconds since midnight appended separated by a dot. Unfortunately, I don't believe there's a way to do calculations in the GitVersion YAML file.

It would be great if there was some way to allow one to specify a calculated value. Or even if GitVersion could be made extensible, allowing others to add "custom" fields to the output of GitVersion through some specified means. Off the top of my head, perhaps a JSON Schema could be defined that would allow you to predictably allow others to define custom fields. Or a YAML file, again with a defined schema.