Ability to configure multiple webhook URLs

[connecteev]

Given that Slack only allows you to send to one channel (or user) per webhook, this package needs the ability to configure multiple webhook URLs, so that I can send a slack message to #my-channel or @my-user using one package.

See #7 here which is related. It also seems like this has been solved by @tigran-cl in https://github.com/tigran-cl/laravel-slack but there is no pull request. @gpressutto5 would be great to integrate that into this package.

[carlmagumpara]

i got fix for this

`use Pressutto\LaravelSlack\Slack;

    $this->slack = new Slack([
      'slack_webhook_url' => 'your custom webhook url',
      'default_channel' => 'your custom channel',
      'application_name' => null,
      'application_image' => null
    ]);

  $this->slack->send('Sample Message.');`

[gpressutto5]

Closed by #19