adding ids to each tree element
#1 list elements now have unique ids
#1 aria-activedescendant is now updated when item receives focus
#1 refactoring using constants and removing unused variables
#1 forgot to minify css
#1 more refactoting
More refactoring. This fixes #1
Merge branch 'master' of https://github.com/longmatthewh/jquery-a11ytree