Jenkins Checkstyle Reporter

This commit contains the checkstyle reporter that can be used to track linting progress with Jenkins Violations reporters

It can be used by adding something like the following to your package.json `"scripts"` property object:

    "jenkins-jshint": "lint-trap --reporter=checkstyle > jshint.xml

cc: @Raynos @sectioneight 

references:
https://github.com/jshint/jshint/blob/3a71ce850c57be8c03599462f42245708387a5f6/src/reporters/checkstyle.js
https://wiki.jenkins-ci.org/display/JENKINS/Violations
https://wiki.jenkins-ci.org/display/JENKINS/Checkstyle+Plugin