PHP code style proposal

Readable version: https://github.com/tristanlins/contao-standards-recommendation/blob/propose/php-code-style/proposed/csr-x-php-code-style.md
I only put the opening brace on the same line, not the closing brace.
So the code folding result in my proposal would be:

```php
<?php
// Comment what happens here if condition is true.
if ($expr1) { ... }
// Comment what happens here if second condition is true.
elseif ($expr2) { ... }
// Comment what happens here if no condition is true.
else { ... }
```

;-)