(#2818) - compaction removes orphaned attachments

Migrated idb/websql to have a new many-to-many table
of seqs to digests, fixed compaction of attachments
in all three adapters, added many new tests.
(#2926) - remove vendor from cordova app
(#2923) - add blob-util to docs
(#2918) - revoke object url for test blob
(#2890) - reduce md5 chunk size to 32768
(#2925) - "10 things" blog post
(#2913) - parallel compaction works
(#2890) - websql: avoid hex() for binaries
(#2932) - fix inaccuracies in attachments guide
(#2934) - add more framework adapters to docs
(#2935) - new_edits=false works regardless of order

This fix ensures that the input order of revisions
to the same document does not affect how those revisions
are loaded using bulkDocs with new_edits=false.
(#2937) - add pouchdb dump/load to external.md
(#2939) - refactor checkpointer to own file
(#2943) - Increase saucelabs timeout
(#2931) - parallel compaction keeps db integrity

Contains two fixes:

1. adapter.js no longer passes the rev_tree to the underlying
   adapter. The adapter is expected to recalculate, since other-
   wise the database may change in the interim.
2. leveldb.js has a global write lock for all readwrite operations,
   similar to how WebSQL/IndexedDB work under the hood. I'm not
   100% satisfied with that, but it's better for the db to be
   correct than to be fast.
(#2185) - Remove allowed failures
(#2957) - Add appcache manifest
(#2951) - fix concurrency in leveldb.js

So I figured out where the bug was coming from - I had
not implemented the writeLock correctly. Took this opportunity
to also use the `double-ended-queue` as suggested by
@calvinmetcalf.
(#2962) - Update map reduce
(#2901) - November release blog post