Integrate Codesniffer

[edgarf]

Integrate https://github.com/squizlabs/PHP_CodeSniffer and do the proposed changes to keep the code standard in a high level.

[regiscamimura]

@edgarf Done. It's pushed together with the branch for PHP7.
@skoshkarev Let's starting using this from now on, just to make sure the code follows a certain standard. To run it, use the command line and run this command (from the root dir):

vendor/bin/phpcs --standard=CodeIgniter /some/file/or/folder/path

And

vendor/bin/phpcs --standard=PHPCompatiblity --runtime-set testVersion 7.0 /some/file/or/folder/path

Please use that to verify if your code meets the standards requirements. Don't need to worry right now about previous existing code, just make sure to use it on new code.