sync_protocol.txt

develop a protocol for syncing databases using a shared file system
  dropbox, google drive, webDAV
single master multiple slave structure
changesets
master saves changesets in db with timestamps
master posts changesets in store with unique id
each slave posts tiny file when it has completed processing of changeset with error/success
if all success master deletes changeset file


Node actions:
  join network request full database
  join network request changesets since date
  request to become master
  takeover master after master disappears from network
  upgrade to master status
  downgrade to slave status

Error conditions
  shared storage is down but network is up
  network is down.
  slave disconnects from network
  master disconnects from network


Can we use OPML as the feedlist and feeds?  Can we add extra attributes to each feed in opml?
If so, then changeset would be OPML + New Items + marked + unmarked [marked and unmarked cannot contain the same id in one changeset]