Change `num_fmt` to `numfmt`

[olivroy]

This is incomplete here.

Just as a test here, but I wouldn't know how to adjust standardize_case_names() to make this actually work.

Let me know what you think

** No strong feelings, will likely end up closing, but giving a go anyway

[JanMarvin]

I have at least two of these functions that standardize. One for camel case and one for color. A third was in the na_strings one. For something like this I’d say a special one is needed for predefined sets. Standardize _numfmt into _num_fmt. Should be possible though must be carried out with care.