add option for additional classes on nav element
add test to see if nav has class
Updated Jen's test and created a test for navClass option change
Changed default navClass from empty string to null
Updated navClass option to control class naming throughout
Whoops, forgot to teardown the option tests
Removed extra class name insertion from original PR
Changed navClass option to className for better naming abstraction
Updated the docs
Updating min jQuery version
--amend
Added missing semi-colon
2.2.0