Adding ability to order documents retrieved via Prismic queries, by enab...

...ling the specification of an 'orderings' string in the YAML front matter used in the rendering of Handlebars templates.
Yes, queries still work and content can still be successfully retrieved from Prismic when the 'orderings' key-value pair:
* Is omitted.
* Is specified as ```orderings: ```
* Is specified as ```orderings: ''```

The only case for which a failure occurs is when the 'orderings' string is invalid, which is the desired behaviour for such a situation.