A post page

There's not much here in the sample post page. Better get to work.

The common front-matter data for all of the files in the posts section are abstracted into a posts.json file so that we don't need to repeat that on every file. Handy.

It looks like this:

{
  "layout" : "layouts/post.md",
  "tags" : "post",
  "templateEngineOverride": "njk,md"
}