Support HJSON

[westonganger]

As described in locomotivecms/engine#1321

Website: https://hjson.org/
Ruby gem: https://github.com/hjson/hjson-rb

HJSON adds the following features to JSON:

• Trailing Commas
• Comments (#, //, /* */)
• Quoteless Keys
• Quoteless String (meh but okay why not)
• Write multiline strings with proper whitespace handling.

[did]

hey @westonganger, I wasn't aware of this gem! Looks awesome but the ruby implementation doesn't have a good SyntaxError exception in the sense that it doesn't report the line number where the error occurs.
I know that hjson is highly permissive so it might look minor but I believe it's important.
I don't mention that other developers would stick to the old JSON format.

Why not enabling hjson per Wagon site? What are your thoughts? Have you already built sites with this syntax?

[westonganger]

Sure we could enable it per project. Maybe we add this key within config/site.yml

### For more permissive JSON syntax we can use HJSON, https://hjson.org/
### when set to true, the `hjson` gem must be included within your Gemfile
hjson: false

[westonganger]

Also I may try to see if we can add line number reporting to the HJSON gem.

• Add line number to error reporting hjson/hjson-rb#12
• Add basic line number and character support to exceptions hjson/hjson-rb#13