new themes cupid, lumen, and superhero
larger preview thumbnails
new favicon
flatly: remove table borders
readable: tweaks to navbar and type
simplex: tweaks to type and buttons
tabs to spaces
remove tabindex
remove table-bordered class from preview table
add panel-default class to panel on test page
api: remove punctuation in theme descriptions
add new themes to index and api
bump version number to 3.1.0+1