Debug trait for format enums

[aarongpower]

I've noticed the various enums in format.rs do not have the Debug trait derived. Is there a specific reason for this? I can see it is for other enums, e.g. the enums in worksheet.rs.

Happy to try a pull request, just wanted to check first.

[informationsea]

There are no reason that format.rs does not have the Debug trait. I just forgot to add. A pull request is welcome.