Added support for markdown files with yaml frontmatter.

[raae]

I have been looking for a project like this so I can have a separate repo for the content of my site. I, however, needed support for more blog style content, ie: markdown files with YAML front-matter.

This is my attempt at solving my requirements and it might be a useful extension of your project so I am letting you know through this pull request.

Tests have been added.

[gavinmcfarland]

Hi! I was looking for something that does exactly this. I tried your fork and I was wondering. Should it check for frontmatter first and if it doesn't exist add the rest of the file's content as the __body?

[raae]

I do not really remember what I did as this is a very long time ago. Will have some time to look into this in a couple of weeks if you would like to collaborate.

[gavinmcfarland]

No worries at all, I appreciate it was a long time ago. Yeah that sounds good. I think I can have a look at it first, it should be as simple as checking if there is any frontmatter and if not, capture the content as one big field.