implement JSON5

[ExpandingMan]

https://json5.org/

I'm sure it would be a huge amount of work to fully implement this, but I thought it was deserving of an issue.

Since it's a superset, my understanding is that this could be non-breaking, with the major caveat that JSON3 might lose the ability to validate JSON for other programs that can only support "official" JSON.

There would likely be significant technical benefits to this: unlike JSON, JSON5 differentiates between integers, unsigned integers and floats which is an obvious major improvement over the status quo. My understanding is that this package already implements some hacks to get around the disastrous typing semantics of vanilla JSON.