jgit-checkstyle

use checkstyle implement incremental check.

with the implement, we can use checkstyle only check the new code in every pull request

main code is clone from https://github.com/centic9/jgit-cookbook

1. git workflow(use jgit) git merge-base xxx xxx //get common commit. git rev-parse HEAD //get current commit
   git diff --unified=0 commit1 commit2 //get diff
2. parse diff
3. update suppressions.xml
4. combine with checkstyleMain task

please see code in DiffFilesInCommit.java and build.gradle