Use Org mode buffer settings instead of YAML

When writing Jekyll posts, we need to include some YAML headers to set the layout and title for the post like:

```
title: something
category: posts
layout: post
```

this works, but ideally I would like to have the whole file using Org mode format. I think Org in buffer settings are a good alternative, so with this PR it is possible to use the following instead:

```
#+title: Replacing Jekyll YAML headers with Org mode buffer settings
#+category: posts
#+layout:   post
```

what do you think?