Added support for the ARABIC excel function

[paulkned]

This is:

- [ ] a bugfix
- [ x ] a new feature

Checklist:

• [ x ] Changes are covered by unit tests
• [ x ] Code style is respected
• [ x ] Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• [ x ] CHANGELOG.md contains a short summary of the change
• Documentation is updated as necessary

Why this change is needed?

[MarkBaker]

Thank you for the contribution

[MarkBaker]

Note that I've merged to master "as is". However, this code doesn't handle short-form valid values like MIM for 1999

[paulkned]

@MarkBaker good point. I'll submit a new pull request for that. If I'm building something, why not build it correctly :)

[MarkBaker]

There's other unusual short-forms; MS Excel's ROMAN() function has a second argument of type (which we don't actually support in our implementation), but which does allow you to see the short-form values