First commit of "Table of Contents" script

+ Introducing Sextant, which builds a Table of Contents for you
(because headings)
+ Add _sextant.scss specific styles to enhanced CSS
+ Add menu icon and button styling
+ Prospectus now auto-handles the ARIA hidden/expanded/owns/controls
states for all dropdowns
+ Rename the global navigation to "Checkov" (it's more global)
+ Add velocity('stop') to all Nav and Whirligig animations so you can't
toggle them 100x quickly

Related to issue #10