Coerce items

[shmax]

Adds support for coercion of items for schemas with a type of array:

$value = (object)[
    "foo"=>["7","9.1","true"]
];
$schema = (object)[
    "type"=>"object",
    "properties"=>(object)[
        "foo"=>(object)[
            "type"=>"array",
            "additionalItems"=>[
                "type"=>"boolean"
            ],
            "items"=>[
                (object)[
                    "type"=>"integer"
                ],
                (object)[
                    "type"=>"number"
                ]
            ]
        ]
    ]
];

echo gettype($value->foo[0]); // "string"
echo gettype($value->foo[1]); // "string"
echo gettype($value->foo[2]); // "string"

$validator->check($value, $schema);

echo gettype($value->foo[0]); // "integer"
echo gettype($value->foo[1]); // "double"
echo gettype($value->foo[2]); // "boolean"

• moved the coercion helpers out of ObjectConstraint and down into Constraint, because there are non-objects that need to coerce
• Got rid of CollectionConstraint. Because we need to pass arrays by reference to coerce them, and because CollectionConstraint was concerned exclusively with arrays of things, its check method was rendered useless. My choices seemed to be to factor it into the base Constraint class (which already had a checkArray method) or change all checkimplementations to take a reference; I chose the former because the latter would mean breaking backwards compatibility (only variables can be passed by reference, so any inline array literals being used out there in the wild would cause a run-time exception). Hope that's not a problem.

@bighappyface @digitalkaoz

[shmax]

Would love some feedback, guys

[shmax]

@bighappyface Is there any chance we can get this merged before #331 ? I'm not looking forward to resolving those conflicts...

[bighappyface]

@shmax I can work with you on that. Is this PR rebased on the latest?

[shmax]

@bighappyface Yep, good to go. No conflicts with the base branch.

[shmax]

I'm working on a complete redesign of the coercion functionality that makes this PR unnecessary.