3.0.1: PHP 8 and phpspec 7 support

* added PHP 8 support
* added phpspec 7 support

PHP 7.2 requirement

Dropped support for PHP <7.2

Other upgrades:

* upgraded PHP CS Fixer (from 2.10 to 2.16)
* upgraded phpspec (from 4.3 to 6.1)

*BC Breaks* - removed deprecated api:

* removed all `make` static constructors

Normalized float to double

Normalization from float to double, thanks to @ItsKelsBoys

Updated test suite

Merge pull request #16 from roukmoute/version-2

Add support for PHP 7.2

Released v2.0.0-alpha3

Return type hints

* added return type hints

Fixes

* fixed PHPdoc return type hints

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')))
;
```

* reverted the FQCN change