New proposal on topic creation and subscription.

- updated the document making topic string as opaque object for projector and
  router.
- made router into a re-entrant component. That is, all the required
  information for a router to function on stream will be supplied during
  stream restart.
- simplified index rebalance.
- added few more words of explanation for missing STREAM_END due to projector
  crash while kv-rebalance.
- cleaned up document and made it relatively more consistent.

Change-Id: I0d347c0185cf214c8bdbc02529e637fd39ccd7e3
Reviewed-on: http://review.couchbase.org/34976
Reviewed-by: John Liang <john.liang@couchbase.com>
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Reviewed-by: Pratap Chakravarthy <prataprc@couchbase.com>
Tested-by: Pratap Chakravarthy <prataprc@couchbase.com>