added a little command to benchmark PHPCR

As can be expected for both insert and lookup by path scale really nicely but search increases severely with more nodes on the same level.

results with jackrabbit:
```
Inserting 100 nodes took '78' ms.
Getting a node by path took '0' ms.
Searching a node by property took '4' ms.
Inserting 100 nodes took '78' ms.
Getting a node by path took '0' ms.
Searching a node by property took '6' ms.
Inserting 100 nodes took '78' ms.
Getting a node by path took '0' ms.
Searching a node by property took '9' ms.
Inserting 100 nodes took '78' ms.
Getting a node by path took '0' ms.
Searching a node by property took '13' ms.
Inserting 100 nodes took '78' ms.
Getting a node by path took '0' ms.
Searching a node by property took '21' ms.
Inserting 100 nodes took '79' ms.
Getting a node by path took '0' ms.
Searching a node by property took '24' ms.
Inserting 100 nodes took '80' ms.
Getting a node by path took '0' ms.
Searching a node by property took '27' ms.
Inserting 100 nodes took '81' ms.
Getting a node by path took '0' ms.
Searching a node by property took '31' ms.
Inserting 100 nodes took '81' ms.
Getting a node by path took '0' ms.
Searching a node by property took '35' ms.
Inserting 100 nodes took '81' ms.
Getting a node by path took '0' ms.
Searching a node by property took '38' ms.
```

and results with doctrine dbal with sqlite:
```
Inserting 100 nodes took '139' ms.
Getting a node by path took '0' ms.
Searching a node by property took '44' ms.
Inserting 100 nodes took '140' ms.
Getting a node by path took '0' ms.
Searching a node by property took '68' ms.
Inserting 100 nodes took '142' ms.
Getting a node by path took '0' ms.
Searching a node by property took '91' ms.
Inserting 100 nodes took '145' ms.
Getting a node by path took '0' ms.
Searching a node by property took '115' ms.
Inserting 100 nodes took '146' ms.
Getting a node by path took '0' ms.
Searching a node by property took '138' ms.
Inserting 100 nodes took '147' ms.
Getting a node by path took '0' ms.
Searching a node by property took '162' ms.
Inserting 100 nodes took '149' ms.
Getting a node by path took '0' ms.
Searching a node by property took '186' ms.
Inserting 100 nodes took '151' ms.
Getting a node by path took '0' ms.
Searching a node by property took '211' ms.
Inserting 100 nodes took '155' ms.
Getting a node by path took '0' ms.
Searching a node by property took '234' ms.
Inserting 100 nodes took '157' ms.
Getting a node by path took '0' ms.
Searching a node by property took '257' ms.
```