Reduce write amplification for partial document updates

Reduce write amplification for partial document updates - only store the part which has changed. This would typically be available when the client has explicitly indicated the part of the document they are changing - either using APPEND / PREPEND, or the sub-document mutations.

(Implementation reference to Storage IO Vectors).

Customer Benefits:

• Higher ops/sec
• Less SSD wear and tear

Dave Rigby, David Haikney please enhance/edit description as appropriate.