Add support for Laravel's dot validation

[felixkiss]

Closes #57
Closes #64
Closes #72

More info: Validating Arrays in the Laravel Validation docs

This PR adds support for:

Dot access for nested arrays

$data = [
    'name' => [
        'first' => 'Foo',
        'middle' => 'Bar',
        'last' => 'Baz',
    ],
];
$rules = [
    'name.first' => 'required|unique_with:users,name.first = first_name,name.middle = middle_name, name.last = last_name',
    'name.middle' => 'required',
    'name.last' => 'required',
];
$validator = Validator::make($data, $rules);

Wildcard access to validate multiple elements in an array:

$data = [
    'users' => [
        [
            'first' => 'Foo',
            'middle' => 'Bar',
            'last' => 'Baz',
        ],
        [
            'first' => 'Homer',
            'middle' => 'J.',
            'last' => 'Simpson',
        ],
        [
            'first' => 'Philip',
            'middle' => 'J.',
            'last' => 'Fry',
        ],
    ],
];
$rules = [
    'users.*.first' => 'required|unique_with:users,users.*.first = first_name, users.*.middle = middle_name, users.*.last = last_name',
    'users.*.middle' => 'required',
    'users.*.last' => 'required',
];
$validator = Validator::make($data, $rules);

[rscmendes]

I get an error when validating arrays of the type "user_id": [1, 2, 3].
For example:
$data = [ "user_id": [ 4, 6 ], "post_id": 5 ];
$rules= [ 'user_id.*' => 'unique_with:post_user, post_id' ];
$validator = Validator::make($data, $rules);

This returns the following error:

"SQLSTATE[42S22]: Column not found: 1054 Unknown column 'user_id.0' in 'where clause' (SQL: select count(*) as aggregate from post_user where user_id.0 = 4 and post_id = 5)"

Am I doing something wrong here? Or is this not supported yet?
Thank you

[felixkiss]

@bluetrickpt You need to specify the name of the column in the DB nanually when using arrays. Like so:

'user_id.*' => 'unique_with:post_user, user_id.* = user_id, post_id'

Let me know if this helps. If not, feel free to open a new issue for your problem.