Deprecate PHP 5, add PHP 7 features

[gregurco]

• [x] Bug fix
• [ ] New feature
• [ ] BC breaks
• [ ] Deprecations
• [x] Tests pass

Fixed tickets: [#96] License: MIT

What I did:

• [x] Add parameters type hinting
• [x] array() to []
• [x] Add classes to use
• [x] Return type to methods
• [x] Readme
• [x] Fix tests
• [x] Fix comments
• [x] Fix typos
• [x] Fix code style

[gregurco]

@florianpreusner could you check this PR? I think it's done. I also added symfony 3.3.* in travis. All checks passes.