Add REM polyfill as submodule.

The rem unit is not recognized by all browsers (ie8-), so this polyfill should convert all rem units in the CSS to pixels.
Conditionally load the REM Polyfill.

Fire up Modernizr to only load the polyfill in situations that it is needed.
Introduce the magic build script tags.

The H5BP Ant Build Script requires special HTML comment tags be placed around all the javascript calls that are to be minified and concatenated.
Move jQuery loading into Modernizr.

Ask Modernizr to load jQuery and handle the conditional local fallback.