Restore mistakenly removed iffs

[kuzkry]

This partially reverts #2356 (it's not 100% revert, I made some modifications to prevent too long lines).

TL;DR: Wary as usual @adambadura (thanks mate, all credit to you ;) ) found out that I made a mistake in #2356 by thinking iff was a typo of "if", whereas it really stands for "if and only if".

For more, please follow the discussion started in #2356.

[adambadura]

@kuzkry, I think it would be better to use if and only if instead of iff. This will prevent the same misunderstanding in future.

However, if comment lines are broken at some column (which seems to be a somewhat flexible rule) changing iff to if and only if cannot be done by simple find-and-replace and requires a manual check of each case to ensure that line length limits are observed.

[kuzkry]

@kuzkry, I think it would be better to use if and only if instead of iff. This will prevent the same misunderstanding in future.

However, if comment lines are broken at some column (which seems to be a somewhat flexible rule) changing iff to if and only if cannot be done by simple find-and-replace and requires a manual check of each case to ensure that line length limits are observed.

Ok, done. I'm keeping this WIP, as I would like you to make sure it's like you wanted it to be. @adambadura, please take some time and be very precise when pointing me to lines that you still consider too long.

Commits and their logic:
1a6d736 is find and replace
2f39f43 is what clang formatting tool thinks about it
f7b850e is a bunch of my propositions

When we're done, I will simply fix the last two and withdraw WIP from the PR title.

[adambadura]

Seems OK to me. I have no particular needs about the line breaking. I just noticed that in general line breaking is used. Although the length limit didn't seem consistent.

[kuzkry]

Thank you @adambadura!

[kuzkry]

Temporarily closing this to avoid a merge conflict with another pull request.