ensures that no browser shows a vertical scrollbar in the code blocks of guides, thanks to Marcelino Llano for a hint to fix this

switches guides code syntax highlighting to the better SyntaxHighlighter, I did my best with the theme, I swear

made a pass in AR's schema.rb to keep (most) create statements in lexicographic order, and fixed an FK

This way parent models can get their own after_create and
after_update callbacks fired after has_one has done its job.

Use render :template instead of render :file in nested layouts example. render :template is a bit faster and more semantic compared to render :file.

changed names to autoload_paths and autoload_once_paths respectively