See #9 for reason

• add rules for PHP 7.2
• add travis test for php versions 7.0 / 7.1 / 7.2

• Add MIT LICENSE file
• Apply CS with new header
• Rename .php_cs to .php_cs.dist

• feat(header): Add generic license header

This header don't set the license type, it just indicate that license is located
in LICENSE file at project root.

• Use Travis instead of Gitlab CI
• Change project name for using Packagist