Remove javascript/main.js as unused
Move layout specification to front matter defaults
Move general page template to _includes

Move general page template to _includes in preparation for adding other
layouts using the general page markup.
Select top level menu items on sub-pages

Make top level menu items appear selected, but active on their subpages.
Add bare tablet page layout
Remove filetype-based directories

Move files from filetype-based directories (images, stylesheets) to the
root directory to leave non-special directory namespace for page
organization.
Add tablets directory

Add tablets submodule directory, along with styles and tablet page
template.