This commit removes the fragile front matter decoding, and takes the provided archetype file as-is and processes it as a template.
This also means that we no longer will attempt to fill in default values for `title` and `date`.
The upside is that it is now easy to create these values in a dynamic way:
```toml
+++
title = {{ .BaseFileName | title }}
date = {{ .Date }}
draft = true
+++
```
You can currently use all of Hugo's template funcs, but the data context is currently very shallow:
* `.Type` gives the archetype kind provided
* `.Name` gives the target file name without extension.
* `.Path` gives the target file name
* `.Date` gives the current time as RFC3339 formatted string
The above will probably be extended in #1629.
Fixes #452
Updates #1629
