More Variables, menu support, quote fixes

• Adds more CSS Variables
  • vertical and horizontal spacing
  • font weight
  • font voice (italic / oblique)
  • Quotes: open/close, border sizes
  • text interactions: line style and decoration
• Corrects issue with multiple block quotes having single quote
• Adds interactive style to abbr[title]
• Adds style to <abbr>
• Makes the mark::selection slightly more accessible
• Adds support for <menu>
• Removes list-style from from nav li
• Adds documentation for new variables
• Improves documentation around how to incorporate into a project