Better documentation fpr advanced queries / filters and more examples

[pwFoo]

This needs better documentation but you can build advanced queries like this:

use \Maphper\Maphper::FIND_OR;
use \Maphper\Maphper::FIND_AND;
use \Maphper\Maphper::FIND_LESS;
use \Maphper\Maphper::FIND_GREATER;

$products->filter([
    FIND_OR => [
        FIND_AND => [
            FIND_GREATER => [
                'price' => 50
            ],
            FIND_LESS => [
                'price' => 100
            ]           
        ],
        'onSale' = 1
    ]   
]);

Could you add more documentation and examples about (complex) filters?