Add support for Scala 2.10.0 and update library dependencies

I'm interrested in this project and did some work.

I've added support for `Scala 2.10.0`.
In order to do that I updated `spray-json` to `1.2.3` and `specs2` to `1.12.3`.
Unfortunately, there is no binary package of `spray-json 1.2.3` for `Scala 2.9.1`
in the Maven repository, so I dropped support for `Scala 2.9.1`.
I'm not sure this change is acceptable for you.

I've fixed compilation errors due to the update.
All tests passed for both `Scala 2.9.2` and `Scala 2.10.0`.