BSONColumnBuilder will store Simple8b blocks in a higher level binary stream. This stream we will keep track of how many consecutive Simple8b blocks we have with a 4 bit count, meaning there can be a maximum of 16 consecutive blocks.

To avoid using too many temporary buffers where we need to copy the data we should change the Simple8b builder interface to return final Simple8b blocks via a callback. When calling Simple8b::append 0, 1, 2 or more Simple8b blocks may be finalized. A callback interface also provides a generic way to test which scale factor compresses best.