Extract constants, clean up doco a bit.
Drop 'batch' for 'autoFlush' and never enable clearBufferOnFail.

autoFlush, the negation of batch, is the property actually exposed on the underlying client.  I see no reason to deviate from that.

Additionally, when batching was enabled we were previously passing 'true' to the second setAutoFlush argument.  This one controls whether or not failed puts are dropped from the write buffer onto the floor after a flush.  *Under no circumstances do we ever want to do that*.
Expose a scan 'caching' (prefetch) property.
doco
doco