(#1973) - Resolve to {ok: true} on destroy
(#1979) - pass limit option to leveldb changes and fix limit + live in http
(#1999) - Localstorage-down to package.json
(#1997) - parse user agent for the perf tests
(#2003) - remove bluebird from browser tests
(#1990) - move allDocs keys query to adapter.js

This moves the allDocs() logic when opts.keys is
used to adapter.js, which allows us to just do a
simple multi-key fetch for each non-http adapter.

This improves the performance of leveldb.js and should
not have an impact on the performance of websql.js or
idb.js.  Plus it's less code.
more idiomatic promise usage