Made changes to support Zepto.js

* Replaced jquery specific `$.ajax(url, options)` with `$.ajax(options)`
* Changed `jQuery.fn.typeahead` with the more compatible `$.extend($.fn,
{typehead: ...})`
* Replaced `window.jQuery` with `window.$` (should work in both
libraries)
* Renamed playground.html to playground-jquery.html (to confirm that it
still works)
* Refactored jasmin tests in Gruntfile.js to `test:jquery` (still
passes)
* Created playground-zepto.html to demonstrate that zepto works
* Created `test:zepto` to run jasmin tests with zepto.js (fails a lot,
so more work is needed)
* Added zepto.js related vendor libraries.