Add some sort of `with_keys` option to `send_json` about lucky HOT 1 OPEN

Thinking about this more... Maybe we can just do deep nested checks? For example, I want to know if the response has a key with a value that's a massive object, but I only need to verify that one of the key/values in that massive object exist...

# {user: {username: "...", slug: "...", created_at: ..., updated_at: ...., preferences: {theme: "dark", size: "large"}}}
response.should send_json(200, user: {username: "...", preferences: {theme: "dark"}})

This would then let me just do a quick few spot checks on an object instead of trying to worry about the exact time on created_at, or building out each object in a sub array and so on.

from lucky.