elementary CSS 2.1.0

# Styles
- [x] Simplify SCSS code and remove unused libraries
- [x] Isolate SCSS from compiled CSS
- [x] Optimize compiled CSS

# Typography
- [x] Include styles for various HTML elements `abbr`, `ins`, etc
- [x] Use Droid Serif for blockquotes

# Form Elements
- [x] Simplify radio and checkbox semantics

# Toggle Elements
- [x] Switch from checkbox to anchor tag for simplified semantics

# Miscellany
- [x] Bring back range and progress elements with jQuery UI
- [x] Add new `nav` element
- [x] Switched to MIT License