Added the ability to extract links from the pages of other users.

$vk->get_playlist;
$vk->get_playlist(url => 'http://vk.com/userLink');
$vk->get_playlist(url => 'http://vk.com/id1'); # http://vk.com/id1
$vk->get_playlist(name => 'userLink'); # http://vk.com/userLink
$vk->get_playlist(id => 1); # http://vk.com/id1