Provide an option to use pooled NIO direct buffers to minimise impact on GC

When the driver is being used with GridFS to serve binary data ('files) over HTTP, the ByteBuffers that are returned are on-heap. Servers such as vertx are capable of directly serving ByteBuffers, using Netty's ByteBuf abstraction. By using on-heap buffers, we place undue pressure on the JVM GC, as the concurrent load on the service (that's using the driver) increases. Please can we have an option at least to direct the driver to use pooled direct buffers. Thanks.