(#2549) - document that the SQLite plugin is passing
(#2547) - document schema migrations

Based on an IRC discussion today, I realized
people don't know that this feature exists.
(#2534) - use less storage in websql
(#2497) - fix attachments in Chrome and IE
(#2466 #2475) - replicate using changes with include_docs

Also, to fix #2475 we use open_revs="all"
so that the URL is not too long.