Batch requests

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The 2.x versions of the PHP driver allowed assembling HTTP operations in the

client without actually dispatching them immediately. Once enough operations

were assembled, they could be sent in a batch to the server.

The PHP driver offered the classes `Batch` and `BatchPart` for this purpose.

These have been removed from the 3.0 version of the driver.

The `Connection` class also had methods for working with batches, namely:

- Connection::stopCaptureBatch()

- Connection::getActiveBatch()

- Connection::setActiveBatch($batch)

- Connection::setCaptureBatch($state)

- Connection::setBatchRequest($state)

- Connection::isInBatchCaptureMode()

- Connection::getBatches()

These have been removed in the 3.0 version of the driver as well.