HFrame will no longer use cdom.attr()
DOMSprocket updates
framer.onClick() now called from event handlers on <hf:frame> and <body>
cache navigation request details on the click event object.
HFrameset is now a DOMSprocket attached to <body>.
When sprockets.start() is called the <body> enteredDocument callback
kicks-off frameset "rendering".
Frameset "prerendering" (everything in <head>)
is handled by HFrameset.prerender(), called by framer.
HFrameset and HFrame `definition` are now set in framer.start().
framer.start() now returns a promise that fulfills when
frameset <head> scripts and stylesheets have been applied.
This promise is used to unhide the viewport.