Merge pull request #114 from jonoabroad/master

Adding warts for List operations head,tail and last
Create sbt-wartremover sbt plugin
Move src/ to core/src/ and sbt-wartremover/ to sbt-plugin/
Add trigger and autoImport to sbt-plugin
Fix the `wartremover` shell script
Update README with regard to the new sbt plugin
Fix Travis
Merge remote-tracking branch 'michalrus/sbt-plugin'
Merge ListOps._ into one WartTraverser

See:
  * https://github.com/typelevel/wartremover/pull/114#issuecomment-50939214
  * https://github.com/typelevel/wartremover/pull/107#issuecomment-50970027
Update README.md