Added documentation for fieldnameprefix property.
Added documentation for fieldnameprefix property.

brianfrankcooper/YCSB,ChristianNavolskyi/YCSB,ChristianNavolskyi/YCSB,brianfrankcooper/YCSB,brianfrankcooper/YCSB,ChristianNavolskyi/YCSB,ChristianNavolskyi/YCSB,brianfrankcooper/YCSB