Refactor code to match current conventions

* Set headings to standard capitilization
* Max of three `=` or `-` when underlining headings
* Fixed property orders to match our linting rules
* Repositioned line comments
* Corrected line comments to be written using the numbered notation
* Cleaned up unnecessary third level headings
* Removed any placeholder classes
* Added a few extra headings for clarity
* Tried to make the variable's introductory bullet list a bit more readable

Conflicts:
	dist/vellum/_lists.scss
	dist/vellum/_typography.scss
Disable *::before/after by default
Add hidden attribute styles
Fix import file name
Make pseudo elements have double colons
Merge pull request #59 from mobify/add-refactor-changes

Add refactor changes