PHP 7

Dropped support for PHP < 7.

This means we now can use:

• scalar type hints
• return type hints
• callable type hint, without having to check PHP version

All make static constructor were created for PHP < 5.6, they're
now deprecated. Here's an example of what to use instead:

(new Method('sayHello'))
    ->addArgument(new Argument('string', 'name')))
;