drill

7a2ea253 - DRILL-1904 - Part 1: Package level docs for the common module and a few packages in exec.

DRILL-1904 - Part 1: Package level docs for the common module and a few packages in exec. Fix line wrapping on package level docs to standardize at 80 character wrap. Patch updated to address review comments. Patch updated again to address Sudheesh's review comments.