add a prepareTransaction method

[ikwattro]

Currently, there is two possibility to send multiple statements in one transaction :

• opening a transaction, pushing queries and commit
• creating an array of (statements + parameters ) and pass it to sendMultiple

The first one is good if you want to be able to manage the same transaction between different runtimes (which is a rare use cas)

The second I find it not really handy.

The approach is to have the following :

$tx = $client->prepareTransaction($conn = null);
$tx->addQuery($q, $p);
$tx->addQuery($q, $p);
$tx->commit();

using the Cypher transactional http endpoint /transaction/commit

there would be no http requests until commit is triggered.