A value type to hold arbitrary JSON5

[callum-oakley]

We should provide a value type in the style of serde_json's.

Prerequisite for #2.

[zonyitoo]

What's the status of this issue?

[callum-oakley]

Not started, but will try and find the time to take a look at it in the next few days. Thanks for the reminder!

[callum-oakley]

@vdonich alerted me to the fact that serde_json::Value works perfectly well with json5, what with serde being interoperable and all.

For example, something like this seems to work absolutely fine:

let value = json5::from_str::<serde_json::Value>(&buffer);

I would still like to address #2 so we can write json5 in a macro, but assuming nobody finds any issues with deserialising in to serde_json::Value I think this issue can probably be closed. (@zonyitoo pinging you in case this is still relevant, I realise it was a while ago!)