Add variadic variable to __invoke

[roquie]

Hi!
I suggest to add variadic variable to __invoke() method.

Example usages (DTO - Data Transfer Object):

$pipeline = (new Pipeline)
->pipe(function ($payload, DTO $dto) {
    $dto['ten'] = 10;
    return $payload * 2;
})
->pipe(function ($payload, DTO $dto) {
    return $payload + $dto['key'];
});

$pipeline->process(5, new DTO);
//returns 20

process method has ...$params

//https://github.com/thephpleague/pipeline/blob/master/src/Pipeline.php
/**
     * Process the payload.
     * @param $payload
     * @return mixed
     */
    public function process($payload, ...$params)
    {
        foreach ($this->stages as $stage) {
            $payload = $stage($payload, ...$params);
        }
        return $payload;
    }

My example (old code, before update): https://github.com/Roquie/pipeline/commits/master

Note: PHP 5.6 required.
What do you think about it?

[sergiors]

Maybe $params = array_slice(func_get_args(), 1); solve the problem with older versions

[shadowhand]

I actually like this idea a lot. Would you be willing to make a fresh PR?

[roquie]

Ok. It will take me a little time.

[roquie]

@shadowhand check it please #45