added getPathBetween method

@Mulkave This adds the getPathBetween method :

Usage

```php
$start = ['label' => 'Person', 'properties' => ['name' => 'Chris']];
$end = ['properties' => ['name' => 'Abel']];
$paths = $client->getPathBetween($start, $end);

// Specifying depth :

$client->getPathBetween($start, $end, 3);

// Specifying direction

$client->getPathBetween($start, $end, 2, 'IN');
```

* you can specify multilabels for a node by passing an array of labels in the 'label' key of the start or end node props

* Not specifying a label nor properties will throw an error

* Default direction is ALL directions

* no default depth

Should this fit your needs ?