Add Persian short month names for %b

[amir-pashayi]

Summary

Adds dedicated Persian short month names for the %b directive.

Previously, %b used full Persian month names, the same as %B. This change keeps %B unchanged and makes %b return shorter names such as فرو, ارد, and خرد.

Tests

python -m pytest

126 passed, 3 skipped

Closes #168

[slashmili]

Thanks @amir-pashayi,

I'm not sure if it's common to see "فرو" as short form of "فرودین"? Or do you see it people use it calendars or in websites?