add `twirlRecompilationLogger` setting to customize logging during recompilation, fixes #17
bump version
needs spray resolver in twirl-compiler to access twirl-api for some reason
Update to sbt 0.13.1

Also, update sbt-cross-building to 0.8.1 which is latest stable version.
Add Scala 2.11 scala-xml module as dependency of twirl-api.

The dependency is added only when Scala 2.11+ is used.