Adding scala 2.9.3 and 2.10.1 for cross version build and an SBT wrapper.

As the title describes I am just adding tscala version 2.9.3 and 2.10.1 for the cross version build. I am including a `sbt` script based on the good work by @paulp *sbt-extras* (https://github.com/paulp/sbt-extras/blob/master/sbt).

Hope this helps.
Thanks!

PS. The reason I am doing this is that i get annoyed when people do the following
 "com.twitter" % "algebird-core_2.9.2" % "0.1.11"