fix(Parameter): allow required boolean with value false

[jutein]

A boolean false is considered as an "empty" value, so if this parameter is required, it will throw an exception

Fix this by checking the type and the value of the parameter

[coveralls]

Coverage increased (+0.3%) to 93.113% when pulling 6866f95 on jutein:master into 020d03b on RETFU:master.

[yannickroger]

You can add this test in tests/units/Parameters.php it should do the trick:

    public function testAssertValueOnMandatoryFalseBoolean()
    {
        $this->newTestedInstance('name', 'boolean', true);
        $this
            ->given($this->testedInstance)
            ->variable($this->testedInstance->assertValue(false))
            ->isNull
        ;
    }

[jutein]

Test added