Speedier jQuery and Twitter widgets.js

jquery.com uses Google Analytics and so sets a cookie when you visit
the site. When you request jquery.js from its CDN, code.jquery.com,
you take a hit from sending your previous GA cookie in the request.

Google's CDN, googleapis.com, never set cookies and so doesn't add
overhead. It also is faster in my unscientific testing of a billion
Command + Shift + R's.

Twitter's widget library has an async snippet to load the JS rather
than a synchronous script tag. widgets.js was before other, important JS
and slowed down document ready occasionally even on a decent connection.