Add --number-separator CLI flag

[o2sh]

refers to #706

Impacted by the CLI flag:

• Number of branches and number of tags
• Number of dependencies
• Number of commits per author
• Number of commits
• LOC
• Number of files

[spenserblack]

Some things to keep in mind:

• Not all separators are at the thousands place, so we may get a request to support other groupings, later.
• There are some numerical systems that look like 1.234,5 instead of 1,234.5.

So, if --format-numbers defines the thousands separator, it can be a breaking change if we need to rename that arg to accommodate other options. We could

• rename --format-numbers to --number-separator or something, or
• change --format-numbers totake names of formats (we might want to look into what other tools call various number formats).

We could even take a number format like Excel does, #,###.00, so that users can define any placement of separators, and what types of separators to use, without having to raise future issues. That might be overengineering for our needs, though 😆

[o2sh]

You're right, my first implementation actually took a localization as an input, but I reverted in 7c6cbba when I found out that num_crate did not support floating numbers as it would have been misleading to users if the decimal character wasn't affected.

I renamed it to --number-separator after your suggestion.

[o2sh]

I think it makes more sense for this value to be a usize 🤔

[spenserblack]

Yeah, that makes sense to me, too.