[PSR-2] Minor formal fixes

[Marc Ermshaus]

Hi.

I am trying to follow the contribution rules as stated here:

- https://github.com/php-fig/fig-standards#github-usage

Here’s a PR for a fix of a few minor formal issues with PSR-2 that have been bugging me for years.

- https://github.com/php-fig/fig-standards/pull/801

Some section numbers were missing a trailing dot (2.1 → 2.1.). Indentation was wrong in some of the code examples (three spaces → four spaces).

Regards

Marc