added a specialized version for norm(DenseVector[Double])
added sbt-idea to plugins
specialize Unit in DenseVector.foreach for better performance
Merge pull request #160 from mengxr/norm

Added a specialized version for norm(DenseVector[Double])
remove natives from default breeze
made a "natives" subproject that will publish
along with breeze.

closes #161
Merge remote-tracking branch 'scalanlp/master'