PHPCS on .info .txt .md and .yml files

Issue #3133703 on drupal.org by jonathan1055.

In devel/commit/242229e phpcs checking of .info .txt .md and .yml files was removed. The reason was "PHPCS should ignore .md files. Avoids fail reports in MRs"

However, there are probably some valid reason for checking all these file types. Many of the coding standards faults could/can be fixed. By not checking any of these file types we risk missing something important.

So there is benefit here in checking exactly what the failures are. It may be that we decide to skip an individual file, or a particular rule, but we need to see exactly what the problem is first.