Add anchors to bullets

Every bullet is anchored with a short `<a name>` tag and includes a superscript `link` anchor at the end. This makes life easier for me when I want to refer people to a particular guideline, such as:

https://github.com/rapid7/ruby-style-guide/blob/add-anchors/README.md#no-and-or-or

When dealing with new Rubyists and their contributions to my project, I want to drop them exactly on what rule I'm talking about when they don't know about the Ruby Style Guide, instead of telling them to scroll around or ctrl-F or anything like that.

This PR implements many of the suggestions in #319.