Make layout examples dynamic and improve route metadata with Express Map

This removes all the specific routes for each layout example and
replaces them with one, dynamic route: "/layouts/:layout/".

This also updates how the data for the nav menu is generated, and adds
a new `pathTo` Handlebars helper for writing URLs to routes, including
the new dynamic layouts route:

    <a href="{{pathTo 'home'}}">Home</a>
    <a href="{{pathTo 'layout' layout='pricing'}}">Pricing Layout</a>
Remove redundant view name and use the route's annotated name
Remove _even more_ redundancy in the routes definitions
Change order of arguments for `routePage()` sugar function
Merge pull request #154 from ericf/dynamic-layouts

Make layout examples dynamic and improve route metadata with Express Map