Add progress function

[norkunas]

Add progress function

[norkunas]

Maybe, but currently I don't have much time to implement that.

[pionut196]

Thank you! I will wait.
Some advices will be welcome!

[norkunas]

It is possible to debug the process stream providing a debug callback like:

$yt->debug(function ($type, $buffer) {
    if (\Symfony\Component\Process\Process::OUT === $type) {
       // read $buffer
    }
});

So you could read the stream output and determine the progress by yourself.

Or you could implement progress($downloadSize, $eta, ...) method with private $progress property and make a PR for it. But keep in mind that you need to provide the default callback to mustRun method #L121 and in that callback call the progress or debug if they are defined.

[norkunas]

Related to #35

[norkunas]

Handled in 30645d4