[Wip] Replace artax with guzzle 

Initial performance on this when running the following code on a single core virtual machine with 512mb was 22.3 seconds

```php
for ($i = 0; $i <= 10000; $i++) {
    $this->pdo->exec(sprintf("INSERT INTO test_table (id, name) VALUES (%d, 'hello world')", $i));
}
```

@Ocramius, What information should we populate the exception with ?
@seut, In what ways can the server respond with a server exception e.g 5xx error ?