[WIP] Page Sorting

@seldo take a peek at this when you have a chance.

Note: To specify sort order for pages in a section, **every** page in that section (e.g. enterprise) must have an `order` property in its frontmatter. If not, the default (alphabetical by page title) sorting will be used.

This is working but I'd like to clean it up a bit before merging it. I'm thinking the entire turn-a-directory-of-markdown-files-into-a-json-object process should happen at startup, rather than in a bin script. This will keep the content munging separated from the server, routes, etc.