[Fix #319] Add anchors to rule bullets

This adds subtle and nonugly link markup to every bulleted rule for ease
of deeplinking.
Merge pull request #338 from rapid7/add-anchors

Add anchors to bullets
Rejustify README.md to 80 columns
Merge pull request #339 from rapid7/justify-to-80-columns

Rejustify README.md to 80 columns