Auto-bulk-writes

[CLOVIS-AI]

Related to #13

Implement a bulk write transformer that performs operations lazily:

val bulked = collection
    .autoBulk()

bulked.updateOne(…) // Not performed yet
bulked.updateOne(…) // Not performed yet 
bulked.findOne(…) // A read would observe that wrights haven't happened yet, so we need to commit all pending writes first