Persistent client-side storage?

Hi, I added a (datomic like) transactor to give bacwn persistence across browser sessions. With this an app can use some default database and whenever tuples are added or removed, the state of the database will be saved to client-side storage. I put in a new example file called family.cljs for playing around with this persistence feature too.

This is built on top of [ydn-db](http://dev.yathit.com/) which woks as a polyfill over IndexedDB, WebSQL, and localStorage (so the persistence should work in all browser environments).

There might be a few kinks to work out but let me know what you think.