Fix allDocs startkey with indexeddb

* fix lower_bound iterator
* improve test for startkey
Merge branch 'master' of https://github.com/daleharvey/pouchdb into 410-allDocs-keys-option
Add allDocs opts.keys test, improve startkey test

* prepare tests before implementation of new option: opts.keys in allDocs
* improve startkey test
Implement opts.keys for allDocs using indexeddb adapter
Fix http and descending option for allDocs, tests

* fixes http and idb adapter
* add simple test for that to test.all_docs.js
Implement opts.keys for allDocs for WebSQL adapter
Implement opts.keys for allDocs for LevelDB adapter
Cleanup and comment changes in idb adapter

* cleanup changes concerning opts.keys in idb adapter
Improve allDocs documentation

* added description of opts.keys implemented recently
Update docs/api.md

Fix typo
Use more generic error messages

Don't create lots of error messages in pouch.js, just extend generic errors
Merge branch '410-allDocs-keys-option' of github.com:neojski/pouchdb into 410-allDocs-keys-option
Add deleted: true for deleted docs when asking for set of keys

* implement that in every adapter
* add test for that
* improve docs
Merge branch 'master' of https://github.com/daleharvey/pouchdb into 410-allDocs-keys-option
Improve docs language, tiny cleanup

* remove some console.logs
* break too long lines
Merge pull request #429 from neojski/410-allDocs-keys-option

410 all docs keys option