Working Sync Process: Squashed bug fixes and redesigning of
GetSyncInfoRequest-Response cycle.

BUG Fix: Fixed bug of target sending the just inserted docs as part of docs changed at target.

BUG FIX: Fixed GetSyncInforResponse. But problem in flow exists. Blocking REQ on client can't accept more than one response. Thus ignores everything after the first doc.

Updated message structs for redesigned GetDocumentRequest-Response cycle.

Minor bug fix in storing seen_ids. Now only storing the seen_id if the doc is successsfully inserted.

Implemented cache at application tier to store changed documents. Completed redesign of GetDocumentRequest-Response cycle.

Remvoed caching system. Instead target stores no information about changed docs. As requested by the source, they are fetched in place. More efficient than caching. Saves a lot of memory.

Fixed message structure creation in record_sync_info step.