[MPMD-166] Plugin fails when switching from 2.7.1 to 3.0.1
- Adjusted the paths to bundled rule sets
- Add a note for people migrating to Maven PMD Plugin 3.0
- Make the link to the PMD rules index versioned, because PMD now have versioned documentation

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1575980 13f79535-47bb-0310-9956-ffa450edef68