Adds PHPCS

Description of this PR shall be improved too :laughing: 

Well, this packs:
- Adds `squizlabs/php_codesniffer` for obvious reasons;
- Tells **Travis** to check code-style via `phpcs` rule on *Makefile*;
- ~~`$this` on `return` is really ugly (IMO), using `self` instead (yes, PHPDoc does support both);~~
- ~~CS/readability improvements;~~ `->` Tweaking docs;
- Also fixed CS in legacy files `test/module/Test/Module.php`, `SampleControllerTestFile.php`, `TestController.php`.

:beer: :+1: