Doc improvements: update version numbers, provide example build.sbt

Hi.  Based on some hiccups I had getting started with twitter-server, I thought I'd make it easier for others to get started.
* updated version numbers to reflect recent releases.
* rather than update versions in docs automatically (I'm new to all of this), included link to CHANGES, so versions should be more obvious to new users.
* included a minimal build.sbt example, using current version numbers.
If you look at what you have here, and what you have above, you'll notice that the syntax is slightly different.  Here, you have two %, and above you use just one.  The %% appends the scala version.