Proposal: Add `match.json(object)` about samsam

[mantoni]

Giving this some more thought, I now think the most intuitive and flexible behavior would be to pass the result of JSON.parse to match(result, arg) where arg is the argument passed to match.json(arg). It could default to match.any. This would mean:

• match.json() succeeds on anything that is parseable JSON.
• match.json({ key: 'value' }) succeeds when parsing the given string to an object that has key with 'value' (and any other keys).
• match.json(true) succeeds for the string true.
• match.json(42) succeeds for the string 42.
• match.json('something') succeeds for any string that contains 'something'.
• match.json(function (result) { /* ... */ }) would match if the given function returns true.