Use promise queues and batch writes for speed

[andrhamm]

• Allows transformations to specify additional options: scanParams function to return additional scan options like FilterExpression, serializeSkip getter should return true if the skip function should be run serially due to heavy async work, serializeForward getter should return true if the forward function should be run serially due to heavy async work
• Uses p-queue (well, the CommonJS fork p-queue-cjs) to parallelize scan reads and batch writes
• Skips record update if the transformed output is identical to the scanned item (uses _.isEqual)
• Logs item diffs