Kirby3 Bolt - a faster page()

I am creating posts for my plugins to make it easier to find them using the forum search and not just the docs search.

Kirby 3 Plugin for a fast Page lookup even in big content trees.

```php
// lets assume 1000 pages: 10*10*10
$id = 'this-page-has/ten-siblings/in-every-subfolder';
$page = page($id); // kirby core
$page = bolt($id); // ~10x faster lookup

// can lookup beginning at a certain page as well
$page = $somePage->bolt($idInTree);

// it's even faster when you look up based on a directory name
$page = bolt('1_this-page-has/5_ten-siblings/3_in-every-subfolder');