farsi.c: Misc. fixes

- Converted some functions to return bools, and changed their respective
  comments to reflect that.
- Minor fixes to a few comments
arabic.c: Comment fixes

- Use C99 style comments everywhere
- Fix incorrect references to return values
Merge pull request #1479 from Pyrohh/fix_comments_and_use_stdbool

{farsi.c,arabic.c}: Fix comments and use stdbool