New branch: async()

[Emanuele Ziglioli]

Hi everyone ;-)

I've been studying the API changes that happened in Objectify 4, and I'd like to steal once more some ideas, for Siena. 

Here's a new branch where I've started working:

https://github.com/siena/siena/commits/async

One of those ideas is to hide Futures wherever possible. One trick is to use a Proxy that calls Future.get() automaticaly whenever a Future<Map> or Future<List> is involved.

In the future I'd like to remove the sync API altogether and just use async().

More changes could be possible with Java 8, although we're always limited by the underlying database API (if using GAE)

See also: https://code.google.com/p/objectify-appengine/wiki/DesignObjectify4