Consolidated HTML5 Tags & Attributes

This pull request is actually three others merged together. I've managed to pull in and merge the following requests:

 - #96 from @andrewle to add support for `aria-*` attributes
 - #98 from @HoffmannP to add support for the `main` tag
 - #115 from @saadatm to add support for the `role` attribute

While this may or may not be the best way to go about getting these features added to the mainline repository, I wanted them for myself and I figured others may as well.