(#2283) - 'destroyed' event has correct db name
(#2054) - implement PouchDB.defaults

This also fixes a few bugs in how opts.db
is used in leveldb.js, namely:

1. the leveldown object was overriden globally in the browser
2. databases with the same names but different backends collided
(#2356) - fix syntax errors in put() docs
(#2347) - add opts.size to fix websql quota bug
(#2335) - add more plugins and better organize external.md
(pouchdb/pouchdb-server#45) - fix default opts on destroy
(#2339) - document localStorage warning in Chrome apps
(#2214) - upgrade browserify and mkdirp