Used Cross-building to support Scala 2.10 & 2.11
Our progress in attempting to upgrade to 2.11

scala-xml is inbuilt at 2.10
specs2-2.3.11 is the first shared release between 2.10 & 2.11
Uppercased some macros to fix compatibility issues
Pinned json4s versions to 2.10 as no release for 2.11 exists
Re-added scalaVersion as that's the main build version.
Took 2.10.3 out of crossScalaVersions as scalaVersion runs in
cross-build mode
Merge pull request #47 from CaseyLeask/update-scala-to-2.11

Update scala to 2.11