Pass document id & rev rather than the whole document

This uses the ddoc_cache support for revisions. It should
reduce bandwidth overhead of copying documents around.
Handle fabric upgrade

We still need to handle direct document passing for older
clients. The new Id+Rev protocol will be a part of a
future upgrade.
Merge pull request #126 from cloudant/23823-rexi-worker-cache

Pass document id & rev rather than the whole document
Switch from ddoc to id+rev protocol for views
Revert "Carry the accumulator through the foldl correctly"

This reverts commit daf62e64ceafa22094308a810ba3b7793a869301.
Revert "Send a `no_pass` message when a doc fails a filter"

This reverts commit 1a639c9d4b3e307addabfa642953ffc3bc675405.
Revert "Update changes workers with new rexi APIs"

This reverts commit abe37938333a59abaee17720450a2923c6ce0482.
Revert "Update reduce view workers with new rexi APIs"

This reverts commit 3da89dee84da62a7585be5223a288008b3658ade.
Revert "Update map view workers with new rexi APIs"

This reverts commit 1a492c7c8d06ad3e86b0b9430e0b57f3fd478b60.
Use new rexi:stream2 API

This removes the need to add logic around starting the stream
explicitly.

BugzId: 24636
Send a 'no_pass' message when a doc fails a filter

This finishes off some old work to get filtered changes to send status
updates when they have a large number of docs not passing the configured
filter.

BugzId: 17709
BugzId: 21851
Merge pull request #132 from cloudant/24636-use-new-rexi-stream-API

Use new rexi:stream2 API
Merge pull request #130 from cloudant/23823-upgrade-fabric-view-protocol

Upgrade fabric view protocol to use id+rev code

BugzId: 23823
supporting different values for RINGTOP.
added hash_id to update_docs
added _hash_id as a document property so it is possible to see this working within Futon.
moved hash calculation to http layer
added hash_id to update_docs
added _hash_id as a document property so it is possible to see this working within Futon.
Merge branch '14728-hash' of https://github.com/cloudant/fabric into 14728-hash

Conflicts:
	src/fabric_doc_update.erl